Foam board insulation is an ideal ceiling material for improving energy efficiency, reducing noise transmission, and creating a more comfortable space. It is lightweight and easy to install, making it an ideal choice for interior ceilings. To install foam board insulation, cut the rigid insulation with a long, sharp knife and press it between rafters or joists. Align the front of the board with the face of the ceiling.
To reduce thermal bridging through studs, you can build a double-stud wall or install a continuous layer of rigid insulation on one side of the wall. For existing plaster ceilings, you can install rigid foam over existing plaster ceilings to decrease heat loss in a bedroom. Expose beams, toss down a layer of boards/sheathing, then add rigid insulation foam over that, with some blocking here and there.
For the XPS option, tape the seams and foam the edges to use the foam board as the air barrier. However, you will have to extend the ceiling.
In Phase 1, install rigid foam (3 inch) and ventilation. Apply a 2 inch layer of foam board on the interior side of the ceiling, then add a layer of drywall over the foam. Cut the foam 1 1/4″ short horizontally and vertically, leaving a gap on all sides. Fill this space with gap filler or “windows”.
Clean the ceiling panels with sheet rock as they are a fire hazard if left exposed.
📹 R-TECH Insulation in an Attic or Ceiling Application
HOME INSULATING TIPS FOR ATTICS How do I know if I need more insulation in my attic? No matter war kind of insulation you …
What is the life expectancy of rigid foam insulation?
Polyurethane rigid foam, with a lifespan exceeding 50 years, exhibits low conductivity due to its closed-cell structure and capacity to withstand external influences such as moisture ingress or air movement.
How to attach foam board to ceiling?
In order to install foam board insulation, it is first necessary to apply an adhesive to the reverse side of the insulation material. This is achieved by creating a pattern with a notched trowel. The insulation should then be carefully placed onto the prepared surface and pressed firmly to ensure a secure bond. It is recommended that a straight edge or level be used to ensure uniformity in the application of the insulation. To prevent air leakage and enhance the efficacy of the insulation, it is recommended to seal the edges with foil tape or foam sealant.
What are the disadvantages of rigid foam insulation?
Rigid foam insulation has several drawbacks, including potential higher energy costs due to unprotected cracks, increased air and moisture leaks, and limited installation requirements due to its need for exposed, open walls. If remodeling existing construction, it may require removing existing insulation and drywall. It is crucial to choose the right insulation for your commercial construction project, considering factors like cost-effectiveness, R-Value, mildew resistance, and flexibility. By understanding these limitations and benefits, you can make an informed decision for your commercial construction project’s long-term success.
Can I insulate my ceiling from the inside?
Insulating a ceiling from the inside involves installing a new ceiling below the existing one, attaching insulation to metal or wooden frames before plasterboard board installation. This method reduces the room’s height by at least 100mm and is messy due to suspending the ceiling, drilling, installing plasterboard panels, and finishing with multi-finish plaster and painting. Various insulation materials can be used, such as polystyrene, loft roll insulation, PIR boards, or high sound-absorbing stone wool.
To avoid the hassle and costs of removing plasterboards, opting for a 2-in-1 product that handles all tasks at once is a smarter choice. Insulated plasterboards are being used by investors to speed up the process of ceiling insulation. These boards are attached directly to the existing ceiling using longer screws.
Does rigid foam insulation need air gap?
Some insulation materials, like spray foam, do not require an air gap. However, traditional insulation materials like fibreglass or mineral wool should follow manufacturer’s guidelines for air gap size and placement. Foil insulation is generally recommended to leave an air gap of at least 25mm (1 inch) between the foil layer and the surface it’s installed on. This allows the foil to reflect radiant heat, provide ventilation, and prevent moisture buildup, which can impact insulation effectiveness. The question of whether an air gap is needed between foil insulation and plasterboard depends on the type of insulation used.
Should interior ceilings be insulated?
Insulation is essential in creating a consistent thermal envelope around a home, ensuring no penetrations. It should be installed in ceilings with unheated spaces, basement walls, floors above vented crawl spaces, cathedral ceilings, floors over unheated garages or porches, knee walls, and between interior walls, especially bathrooms. Ceilings and attics are good places to start, as they are accessible and more heat escapes through the roof than any other part of the home.
Common products for attics and flat ceilings are R-30 and R-38 fiberglass or mineral wool batts, which are full width and ensure insulation fills spaces between ceiling joists or bottom chords of trusses. To achieve R-values of R-38 and higher, two layers can be used and their R-value combined.
How to put insulation in an existing ceiling?
It is essential to ensure the appropriate spacing of ventilation, extractor fans, downlights, and piping, as well as the correct positioning of insulation beneath electrical cables wherever feasible.
How do you stick foam to the ceiling?
T-shaped carpet pins, also referred to as upholstery pins, can be utilized to affix foam tiles directly to a ceiling surface. The lightweight nature of these panels facilitates installation, as the T-shaped end provides a secure hold, preventing the panels from falling out.
Do I need a vapor barrier with rigid foam insulation?
The necessity of a vapor barrier in foam rigid insulation depends on the specific situation. In colder climates, an extra vapour barrier is often recommended to prevent moisture from penetrating the insulation layer, which can lead to condensation and damage. In high humidity areas like bathrooms, laundry rooms, or kitchens, a vapour barrier is typically recommended to prevent moisture buildup and damage.
This is especially important for PIR foam insulation, as the foam material can absorb moisture and potentially degrade over time, especially at joints or gaps where moisture can infiltrate. In summary, the necessity of a vapor barrier depends on the specific situation and the specific needs of the insulation.
How do you stick insulation to the ceiling?
Insulation batts can be installed between ceiling joists using a long stick, ensuring they fit snugly without gaps. If underneath isn’t feasible, insulation can be installed from within the roof cavity. If the roof cavity isn’t accessible from a manhole, temporary roofing material removal can be done. Preloading the ceiling with insulation is recommended, and avoid installing during the hottest part of the day as the roof space can reach high temperatures.
Do you need a vapour barrier with rigid foam insulation?
The necessity of a vapor barrier in foam rigid insulation depends on the specific situation. In colder climates, an extra vapour barrier is often recommended to prevent moisture from penetrating the insulation layer, which can lead to condensation and damage. In high humidity areas like bathrooms, laundry rooms, or kitchens, a vapour barrier is typically recommended to prevent moisture buildup and damage.
This is especially important for PIR foam insulation, as the foam material can absorb moisture and potentially degrade over time, especially at joints or gaps where moisture can infiltrate. In summary, the necessity of a vapor barrier depends on the specific situation and the specific needs of the insulation.
📹 Getting R-30 in an attic suite with 2×6 ceiling rafters
This video demonstrates a DIY method for achieving R-30 insulation in an attic with 2×6 rafters. The creator uses polyurethane foam boards to achieve the desired insulation level, explaining the process of installation and sealing gaps. They also discuss the importance of ventilation and the cost comparison between foam boards and spray foam.
This is a good book. Does provide a step by step introduction to how to build things youtube.com/post/UgkxhgbP-6hUnXu_QRaoHgLztgsI0YF3HqR0, also does offer some steps. Includes pictures to give you ideas for layouts and such. If you are looking for a guide, this is not exactly what you want. But if you are trying to familiarize yourself with the way that pole barn building and other out buildings, are made, then this will work just as you need it to. A few things in this book are a barn (of course), detached garage, storage building, and coops.
I did a project similar to this. A problem that occurred with it was that our vapor barrier got punctured allowing bathroom moisture into the insulation cavity. One wiring penetration wasn’t tightened up. 5 years later there was moisture in that insulation space and some rot in the roof deck. Roofer found it. We went back and fixed it. You can’t be too careful when you insulate in a space like that, especially if there is a shower in a bathroom or a kitchen. Venting moisture sources is so important.
Hi Dave, thanks for this vid. Last Nov 2019 I applied your technique in the porch ceiling of my home and made it into a cathedral ceiling! I want to thank you for caring to prepare and edit and share your article. Throughout the layering of insulation I incorporated two different layers of bubble foil for radiant heat effect. 🙂 You rock! Imitation is the best form of flattery. This proverb imitation is the sincerest form of flattery means that one imitates someone else because one admires that person or values what that person is doing. Cheers from Atlantic Canada during Covid pandemic 🙂
thank you. this is great. There was 0 insulation between Rafters in my place and I installed a Sika 1/2 inch Insulation below Roof Decking between rafters, with a 2 inch air gap below it, to at least have something. Used strapping above insulation as spacer – and below it to hold it in place. Attic has No ridge vent, and won’t have one ( historical home / not dealing with the association) so I stopped the insulation 8-12 Inches from the roof ridge to avoid creating a heat bomb at the ridge. Will install Gable vents on either side of the attic to help move the heat out. While installing, when my face is right in front of the insulation and air gap, I can feel the heat. It’s amazing. Also installing insulation between joists above all ceilings. Attic is not a living space, and not for storage, but it does have flexible A/C vents run through it, and Air Handler for AC is located in attic too. Hoping this moderate Sika 1/2 inch R 3.2 install with Gable Vents will reduce the “oven effect” in the attic.
Your article gave me the idea, i went on hunt for the best r value foam and found polyiso which is like r-27 for 4 inches. I luckily stumbled upon guy selling johns manville 4″ polyiso 4’x8’ sheets for.40 bucks each. I got 40. To cut i found what was best was using metal blade fine tooth on a sawzaw. I measure the top, mid span, and bottom, put straight wood on the polyiso after making the 3 measurement marks. Then using clamp on top and bottom i clamped the wood on the marks which gave the sawzaw a fence to go along so i got nice straight cuts. Often it was a nice snug fit, sometimes i had to do a little extra trimming. I only went with 1/2-3/4 inch air gap, which allowed for 1/2 inch foam board on top to fill in the bay. I could run another r-10 rigid foam on top of that giving me close to r-38. Think we going to do knotty pine tongue n groove on the angle ceiling pottion. Our flat ceiling area is 9 feet.
I have a friend that does flat roofs, they use this exact insulation board on the roof before the rubber roof, he was talking about how high the r value was, I was building living quarters on a garage I already had, and I bought about 1500 sqft of these insulation boards from the company they used. I had it stacked on my trailer in my garage intel I was ready for it, I walk in there one warm day and the fumes coming of that insulation smelled terrible, it was so bad I thought no way em I using that in a air tight living space If it smells like that in this 50×50 with 16 ft ceiling garage, after doing some research and talking to the manufacture, this insulation is not certified for interior use, it’s sold for use on exterior of building, it is not Certified for indoor air quality requirements. I decided against using it, and sold it. It’s now on the exterior of another Friends roof he used it under a metal roof.
Well done!!!! Where we live it is R22 on the diagonal & Vertical & R60 in top horizontal (Attic). Never thought of using your method and it is indeed a sound solution. Just as effective as sprayfoam but without the cost and possible off-gasing (if the two chemicals are not mixed just right). If I ever have to do this again I will copy your solution! Bravo
I own a 2600 sqft cape with a walk-out basement, I had all exterior walls including exposed basement walls, the ceiling of the 18′ dormer, and rim joist spray foamed, cost me $7500 including labor. Well worth the cost here in NH. I recommend you get a quote from your local insulation company before you insulate anything because they beat the cost of insulating my garage by $300, labor included!!! I quoted out the cost of the insulation from Home Depot and they came in $300 cheaper including labor, so I didn’t have to deal with getting itchy, sweating my ass off, or breathing in any of the glass. The insulation companies buy the product wholesale which allowed them to quote cheaper than the big box stores including labor. Dave did a great job here and I’m impressed by how nice the job came out, but time is money so you need to include your time as well in the cost of the job, not to mention your health.
Agree with the hot knife comments, no dust, clean edge, super quick, inexpensive. Gonna have to redo all your nailers if you’re sheet rocking the space. Whatever you do for the ceiling it’s gonna need like 4″ screws just to reach the rafters. Better off packing out the rafters first, insulation next, then interior framing, electrical, plumbing, etc..
Your article is great, it is drawing out a plethora of comments from which we can overthink everything. We think you did a great job and credit you for pioneering this system. A friend did well with a cold roof design 20 years ago. (Your 1 1/2″ spacing kept his shingles strong). Our plan was one layer of foam board followed by spray but you showed this to be more economical.
Dave, What zone are you in? I like the idea but two things – where do you find this stuff? And second, is it safe to have that paper packing on the foam when you are layering it? It’s a common no-no to have something like faced poly-iso stacked because you trap moisture in between two layers that can never evaporate once you seal the gaps. Same principal with laying paper faced fiberglass insulation on top of paper faced fiberglass insulation. Nice work, be sure to invest in a $30 respirator so your lungs don’t kill you from those particals.
Just read over a lot of the comments, and here’s some more info … I cut the foamboard outside and wore a dust-mask too. I’m in zone 3 R-30 is code for ceilings where I live. This is permitted and inspected construction. I told the inspector my insulation plan before-hand and he approved. It passed inspection and is now covered in finished and painted drywall. The insulation is GAF Energyguard. I could not find the board for sale online, but purchased a pallet of them from a local roofing supply company (ABC Supply, Greenville, SC) for less than $20 per sheet. gaf.com/en-us/roofing-products/commercial-roofing-products/insulation-cover-boards/cover-board/hd-polyiso/energyguard-hd-cover-board These particular boards are usually used in exterior roofing applications, but I confirmed with the dealer that I could use them how I did. The boards are polyisocyanurate covered with a vapor permeable fiber-reinforced paper. The inspector required 1.5 inches ventilation space between the insulation and the roof regardless of what type of insulation was used (including spray-foam) (*edit: unless my shingle manufacturer okayed no ventilation. They did not.) That is why my last layer is across the rafters. I would have rather it all been inside the bays and had the headroom instead of having a thermal break, but had to do what I had to do. Thanks for the comments. A lot of good suggestions out there. **WATCH THIS BEFORE YOU CUT FOAM youtu.be/Z292iuV91hA
2021. Lot of work but it will definitely do the trick. Actually not polyurethane but polyisocyanurate insulation. Suggestion. Go to any roofing supply house (ABC Supply) to purchase the insulation approx. $56 per 100SF for 2″ or $83 per SF for 3″ and do in 2 layers?. (save a lot over HD or Lowe’s) and also buy 3″ insulation plates in lieu of 1″ washers. Steel plates cost approx. $110 per thousand. Plastic plates cost approx. $125 per M. You can also purchase insulation screws especially made for polyiso insulation. 7″ screws will run you about $225 per M. Bottom line material cost approx. $2 per SF. 40-year commercial roofing contractor.
Problem is you didn’t get R-30 in the rafter space, so your Title is misleading. You ended up putting 2″ of foam board across the rafters, which means that when you put 1/2″ sheetrock to cover the foam board, you will have to use 3 1/2″ sheet rock screws to reach the rafter and have enough screw left to bite into the rafter. Should have just padded the rafters down 2″ with 2x material and leave 1 1/2″ of airspace under the roof deck. Padding down 2″ with 2x material gives you a 7 1/2″ rafter space which after filling with 6″ of foam board allows you to screw sheetrock directly to the padded rafter with standard sheetrock screws. In essence you padded the rafters down 2″ with the foam board, so no change in lost headroom by padding the rafters with 2x material.
I recently bought a home that was built in the 40s (2×6 rafters), and I want to add a finished suite exactly like you are doing. One concern I have however, is my house has no overhang/no soffit for ventilation. I feel my only option here is to do an un-vented/hot roof. Would I still need to leave that gap of air space, or would I be fine to just run everything flush to the underside of the existing decking? The other issue I have to deal with, is at some point new sheathing was added over the top of the original planks on the roof, so there are hundreds of nails that were shot through both layers of sheathing, but they are sticking out in-between the rafters. For that reason, I was thinking about putting R-19 unfaced batts between the rafters, and then installing 2″ R-13 foil faced rigid over that (similar to how you constructed your third layer of rigid). The foil faced insulation would then act as my vapor barrier. I would run this from the ridge all the way down to the subfloor, so I am even Insulating the crawl space behind the knee walls (leaving the knee walls uninsulated). This would give me R-32. Does anyone see any issues with using the batts instead of the rigid between the rafters, and should I be leaving an air gap, or am I okay to push everything right up to the underside of the decking?
Thank you!! I’m a bit of a DIYer – redoing a master bedroom in a bungalow up in MA – 4×6 rafters. I was going to go closed cell spray foam because I didn’t want to lose headspace, but it’s so $$$! This article has completely changed my direction. Found R13 2″ polyiso board – 3 layers will get me up to a compliant R 39 in my area and it will save me THOUSANDS. You are the man!
This is the best job I’ve seen yet. Did you consider a sealant or coating (maybe aluminumized) on the underside of the roof. I was thinking that so much hot humid air is going to be moving through these conduits that protecting the wood would be wise. I was also thinking about using a foil faced foam to reflect more of that radiant heat back at the roof.
Building codes are really getting out of hand. What happened to being able to build and or/renovate your own property without all of the governmental authorities controlling every step you take. I understand that there are some foundational and potential safety concerns, but its really getting out of control with the amount of influence and authority that is being imposed on a property owner. Today I am a general contractor, with some 24 years experience in the construction and skilled trades industry, but was also an inspector for a local city government….couldnt stand it. I was sickened by what we were being required to enforce on hard working individuals either trying to make a living themselves in construction, or a homeowner that just wanted to improve their own personal property. So I resigned and went on my way
Not a fan of foam over the rafters and then screwing the sheetrock through the foam and then into the rafters. I’d build the rafters down with 1.5″ x 2.5″ filler strips with long (4″) drywall screws and adhesive, leaving a 1/2″ space between the boards and sheetrock.. Your sheetrock will remain more stable through the season changes. And you’d net out very close dimensions.
Do you have soffit vents? I want to insulate my roof and I’m trying to figure out the best way. I have no soffit vents nor do I have a ridge vent. The only vents I have are one on the west side of the roof and one on the east side of the roof about one foot away from the ridge. Do those two vents vent enough? Is there even a need to keep those two vents if there is no soffit vent? Any insight would be appreciated.
Best way to cut this poly-iso board without making a mess… Just sharpen the side of a thin putty knife. It will zip right through it. Trust me, last thing you want to be doing is cutting this with a saw…. They make special blades for doing it that are dustless,… But the putty knife will work just fine.
Just foam it. Leaving an air space invites moisture-laden air to condense inside of the cavity. University of Dayton had this problem, removed all the insulation, foamed 4″ of closed-cell foam on the underside of the cathedral roof deck. Everybody happy, and all good. Montgomery County building department (who had originally insisted on an air space) admitted they were wrong.
R 30 fiberglass between rafters leaves you an effective R 21. By adding 1 layer of that board across the rafters you would have an effective R value of R 32.5 but lose 2″ of head room. The way you did it you did get 11.5 x 3 layers = 34.5 minus for the wood of 5.5. So 34.5 – 5.5 = R 29 but hey, you didn’t lose 2″ of head room. Good Job? BTW you are lucky, here where I live ceilings have to be R 42
At all rafters you have reduced R-value at about R11 vs R30 for in between the rafters. When you see a calculation of the compounded R-value of a wall with thermal bridging you would be surprised by how much the overall R-value is compromised by the areas of the rafters. I didn’t do the calculation but wouldn’t be surprised if your overall value went down to something like R-25. Still not bad. A very clean way which involves getting a new roof in outside insulation on top of the sheathing. There is a lot that we could improve in roof construction in our country. It took literally decades for people to generally realize that a rainscreen is far superior to a conventional wall construction. The same is true for roofs. Maybe I will do a article to explain how this works….
Actually you don’t beed ventilation if … you don’t have vented soffits or ridge venting. If you have only vented soffits but no ridge vent you have no draw to pull airflow so your better off eliminating any soffit vents and completely filling each cavity from the roof sheeting to the inside face of the rafters. I know what I’m talking about and have done insulation for many years. I’ve argued with engineers and architects who were ignorant of the facts and hated being proved wrong by some blue collar worker. If you think completely filling the cavity is crazy then think about this,,, are your wall vanities vented? How about any floor insulation? Not so crazy now is it. As long as there are no gaps, moisture won’t be a problem.
Hello Dave, I really liked how you insulated your attic’s rafters with the foam boards. Is there a reason why most people using these foam boards in attics only use them on the rafters and not in between the joist that are normally filled with loose blown-in insulation? Is there a reason not to use those foam boards in between the joists and then blow some insulation one them. Thanks, Juan
In our area, home dep. sell a 2″ thick iso board rated @ about R-13+, that has a heavy foil face on both sides. I’d advise sealing the edges using a good foil tape if edge is exposed. Our attics are Code @ R-40. Unfortunately, most common roof framing is the cheap trusses, which have too-narrow an eave angle to fit even R-20 nearer the wall edge. It’s tricky retrofitting that for better insulation. Here, we plan to push-out walls under the eaves, to gain interior space, and install exterior insulation..which will also help those narrow angles in the attic periphery be better insulated. Strategic deco ceiling-to-wall Coving at those edges can also camouflage more insulation there.
Instead of using polyiso insulation-switch to XPS OR EPS. I work in the roofing industry and we only use this polyiso with fiberglass facer because the facer is made to have stuff stick to it. We use extruded (XPS no facer) or Expanded (EPS (styrofoam)because it doesnt have the fiberglass that irritates skin and lungs
“R” values measure only what the companies that make wool type insulation want. Heat transfers through conduction, convection and radiation. “R” value only addresses conduction in a very imperfect way. The test is in a controlled setting with no air movement, no radiant sources and is done is just a couple of hours. Wool insulation does nothing for convective or radiant losses. In fact, when cellulose (shredded paper) or foams are subjected to the same torture tests for an extended period (say 24 hours) their conduction losses are the same as the wool insulation tested for the same period of time. The foam and cellulose block almost all of the radiant and convective losses. To see the difference, go to a good supply house and place your hand under the wool insulation with a heat lamp above it and then place it under the heat lamp blocked with wool type insulation. Unless you have to have your work inspected, just use foam board and spray foam and be done with it. If you do need to go through the inspection process, see if the approving engineer will approve a different insulation scheme. If not, hire your own professional engineer to approve and monitor your work. In the long run, it’ll be cheaper and most importantly, you’ll have a better job. My heating bills have been reduced by at least half since I started doing it this way. I’m in the process of tearing out all the wool type insulation in my home and installing foam boards.
Close cell foam must be pretty expensive in your area. Our company has had 2×6 bays filled with close for about $2,000 for a ceiling about that size. You still have to go back and strap the ceiling which you didn’t include in your total cost. The labor and materials for what you did seem to be less than cost effective. The spray job would have been superior.
Wow…Being rich must be awesome!…:)…Great idea though!… The cost for R 30 Batts runs about 2 Bucks a square foot installed…Did you figure out the cost per for this?…it looks like a killer building envelope for an attic…You could heat that whole thing with a small space heater or cool it with a small unit…
Now for me i would have threw R23 rockwool in the gaps THEN going in different direction hit it with Rockwool comfortboard then no need to spray foam anything. Can use caps and screws to hold comfort board up. Cool thing is it breathes, resists moisture and it’s fireproof. That iso board will burn toxic if it catches and doesn’t dry if any moisture gets around it.
Depending on the inspection the ISO board may require a vapour barrier. 2″ of polyurethane Sprayfoam is considered a vapour barrier but 2″ of Iso board is not. The product he is using is a polyisosyanurate. A polyurethane is a polyisosyanate, both products derive from polyol and MDI but are two different types of foam. It’s the gas trapped in the cell structure that gives it its r-value and effectiveness. Polyiso actually preforms worse if not at all at below zero temperatures. Although a decent product for exterior roofing applications and mostly used in commercial roofing a polyurethane Sprayfoam would have been a better option or at the least a true extruded polyurethane board.
I’m working on the insulation for a new shed. I’ve used I joists for the rafters and I’m using foam board (expanded polystyrene) in combination with mineral wool batts. My foam board is looking similar because I’m setting it against the underside of the top flange on the rafters. This gives me an air gap under the roof sheathing. I’m wondering how this setup is aging for you? Have you noticed any moisture coming into the space from that air gap? Is the space always heated?
Not finishing out the bottom and then just putting batts in the ceiling basically defeats the purpose of how you did this. The vented roof will blow cold/hot air thru the batts and the knee wall greatly reducing the r-value. You want to seal off the whole space to make it conditioned. Even just using one layer of rigid foam on the bottom portion of the roof and up top before adding the fiberglass batts would help alot to stop the air infiltration. Putting the fiberglass batts between the rigid foam and the drywall will make sure you get the stated r-value.
How did the total cost of this work out? The current cost of the insulation board is now much higher, but assume your cost of $18 per 4 x 8 sheet (excluding sales tax). That’s $0.5625 per sq ft for R10 of insulation, or $1.6878 be sq ft for r30. Lets say the house is 2000 sq ft, so the roof coverage would be, say, 2,600 sq ft., or $4,388 for the insulation board. Add to that the cost of the wood spacers, wood glue, spray foam for the cracks, the other installation materials, the inevitable additional tools and supplies as well as the “opportunity cost” of the installation time. But you do have a vented roof which will not void shingle warranties. Spray foaming the entire roof may void shingle warranties.
I used this exact material for my house addition. Fortunately, a manufacturer is only about 10 miles from me and sold “seconds” for a fraction of the cost of new. I saved myself thousands, but it was a lot of work and a itchy mess. I filled 2×10 rafters, so my R value was over 50. FWIW, a table saw works well to cut the material.
Great ideas! I will copy your idea of spacers from ripped 2x4s and foam board. HOW DID YOU FASTEN DRYWALL to the living space side? It seems in other articles that you have fully finished out the space with drywall? Long screws to reach though the last layer of foam into a rafter? But can you hang drywall with that? Dont drywall screw heads have a shape to countersink effectively without pulling though?? Did you just use long screws?
Here we have to put in attic vents (insulation baffles) between the rafters to allow air flow from the soffits up to the inside of the attic. Personally I would have ripped down some strapping pieces and tacked them on the rafters to increase the depth then used regular batt insulation. Polyiso foam works worse in colder temperatures which is why it is useless in Canada.
late to the game seeing this, but thank you for the info! i have been scouring for info about this kind of project and very little out there. i did have two small questions based on the end of the article in case someone can answer. when you said batts, did you mean the fiberglass (pink) batts? if so, would using faced batts be a need to fasten within the new studs? would a friction fit material like Rockwool work as well? thanks to anyone in advance!
Just think of air and portland cement with sudsy soap foam mixed in proper proportion. Once mixed it looks like colored shaving cream. I can tell you this stuff is the best bang for your buck. You can not get better and easier to apply. Just mix and pump and done. The R value is 3 to 6 per inch. This ia all determined by the air bubbles size which will determine the density. Good luck too
Hi, this is exactly the idea I was looking for. Thanks for sharing this. My rafters are spaced with the gap being 14-15 inches. What do you recommend for cutting the 8×4 iso panels? Go 12 inches wide and get 3 out of a sheet and fill the gap left and right with spray foam? Did you fasten the first two layers separately, or all three with the rafter screws at once? Thanks in advance! Herb
PIR boards made by Kingspan have thick aluminium foil on both sides, therefore I’ve found that this type of PIR board is the best to work with. But anyway – I would create a ventilatiom gap underneath the roof using OSB3 tongue+groove 15mm boards and the 400mm gap for blown in thermoinsulating cellusose covered by 12,5mm Fermacell board. Estimated R40 ensured 😎😇
I have many decades of renovation experience. This is a good solution. Do you have to cover this for fire insurance? Also, I would always want a vented roof for cooling and moisture removal. 1.5″ seems to have become a standard but my guess is 0.5″ would give plenty of venting. A cutting tip: a diamond masonry saw makes a lot less dust.
This is far from cheap, I would use Rigid foam board, no fiberglass in it and cheaper than iso boards, it is about the same in r-value. To help prevent itching use baby powder, I fill all my pores with the powder including face and neck keeps fiberglass out of your pores and you will not itch, the worst part of the fiberglass dust is when it gets in your eyes and throat.
For anyone perusal this. Do not insulate this way. Don’t insulate the slope then the kneewall wall and floor. Insulate the slope from the soffit to the attic flat. Unless you absolutely have to. Yes it’s slightly cheaper to do the wall and floor. No it’s nowhere near as efficient and you’ll save more in the long run by going down to the toe on the roof deck. And don’t use Batts on the flat, rent a machine to blow it in. Your energy bill will thank you. There’s nothing really wrong with how this guy did it. It’s just the lazy way to insulate these areas and is much less efficient than bringing insulation to the soffit and using blown in in the attic flat where you’ll save more over time. And if you do it his way. Put some tyvek on the backside of the wall and floor to prevent any windwashing on the Batts.
This works if you are able to sacrifice ceiling height. There are 4.5″ R30 insulation boards but, naturally, no big box store will order them and they’re only available from distributors that (so far in my experience) will only sell to insulation professionals/contractors or you have to buy six pallets worth for almost $7,000. Considering R30 is code and a LARGE NUMBER of homes are built with 2×6″ rafters, I am BAFFLED that R30 foam board is not in Lowes/Home Depot/Menards/etc on the shelf. Absolutely annoying.
Creative and it works. However if I am not mistaken R30 code would be on new construction and older homes could be grandfathered. With older homes there is sometimes no way to meet current building codes. Honestly for the time and materials involved you probably could have paid for open cell foam applied directly to the roof deck that would have outperformed that rigid foam just due to it’s ability to stop airflow.. The figure you mentioned seemed high. I had a silimar project in our last house for the master bedroom. About 600 square feet and it cost $1500 for ceiling and walls. I wouldn’t even think about any other type of insulation at that cost…
question on the 1&1/2” gap below the roof deck. Is there a specific recommendation on the size of this gap. I have a very similar situation – but have 2×4 rafters (90yo house) – so I would like to make it as small as possible to get highest R possible – but still maintain deck ventilation. How do you deal with vapor barrier – especially around the interior walls that run along the rafters? – thanks!
add attic vent air baffling against the rafters (this is to prevent condensation against the backside of the roof which must be the same temperature as the outside air.)… use staples. 2×6 Roxul insulation is R24… so you have to find another R6 with a 1″ styrofoam board = done = R30 add 1×2 strapping against the rafters and you’re ready for vapour barrier, drywall etc.
I’d really like to see this at the top and how you seal it (or not). I want to use something like this or 2″ poly-iso foam in our attic which is a 2×4 truss system, so I only have 3.5″ to work with and thus would only do one layer or two. We also have 6″ of blown in insulation on the ceiling. I also wonder why you would not use foil backed foam on the top layer as a radiant heat barrier? Radiant barriers with an air gap work wonders. Regardless, how do the 1.5″ air websites vent out at the top?
Very nice work. What State are you located in? Getting ready to do this myself. Should I be able to achieve the same thing, R-30 with using the 4.5in Thermasheath 3 insulation boards that I’m linking below? And to keep the roof vented would I be able to install 1in rafter baffles before installing the 4.5in Thermasheath 3? rmax.com/thermasheath-3 Thanks
We have recently done a similar insulating job. However, we used Super-Tuff R (I think that what it is – not where I can look at the moment). Also a fiber infused foam – and this stuff won’t burn. Anyway, why did the inspector want 3 layers? I understand that they are “rated” as R11.4 – and you need R30, but foam insulation that is foamed to the rafters is a sealed system and the performance just isn’t equitable – the sealed foam is much better. I looked into having spray foam companies do our roof and walls – and they said 2 inches was all they recommended as anything beyond that is just not economical as the gain in insulative value is minimal for the great additional expense. In other words, if you had put a membrane in there to leave the 1.5″ gap, and had it spray foamed – likely – the inspector would have passed that even if only foamed 2″ thick. You are effectively doing the same thing as you are foaming the edges and still creating the same seal as the spray foam method – you are just using pre-fabed foam as the bulk of it. We don’t have inspectors in our area – no building permits related to building code. I only did a single layer of the 2″ – but recessed it up into the rafters 2″ so that if I wanted to add another layer I could. But, so far, with the space above being vented and using a gable fan, I have not found it to be needed so will leave it at the 1 layer. Just curious if this discussion came up with your inspector and what his rational was for still requiring 3 layers.
Having a house from 1900 it’s not recommended to spray insulation. When buying the property two years ago knew I’d add an attic room, but needed to learn how. It’s not as easy as I thought. With the Derecho storm hitting the property at 140 mph insurance with USAA is covering the roof, fascia, and new gutters. The contractor is sealing it so can add insulation and make it a room. So, that problem was solved with as little as my insurance deductible 😁 Older houses have great high-quality beams, but as you note not wide enough. Thankfully, the property has a pyramid-style roof, but don’t wanna sacrifice height since I’m tall, and for future generations wanna ensure it’ll suffice. This method is gold. I theorized and plotted with research, but nothing came close to this tutorial. Thank you for the wisdom and ideas. For here the energy inspection recommended a 36R value. I didn’t call to ask for city rules. Thanks for the info.
Poly iso is great at warmer temperatures, but its insulation value drops below 50F. Above 50F, poly iso has an r value something like 7 per inch. Below 50F its r-value drops from 7 per inch to 5 per inch and lower as the temperature drops. The inside panel will likely maintain a higher r-value when outside temperatures are colder, but the outside-most panel will have a much lower r-value. On the other hand, polystyrene’s r-value increases at lower temperatures. For cold climates, a good strategy would be to use polystyrene on the outside of the insulation and poly iso on the inside.
you could of just used r15 batts in rafters (they would leave about 1-2″ of space at top, and then ran 2×4 perpendicular to your rafters and put in a 2nd layer of r15 batts. Sure your way saves a couple of inches, but it also probabably costs 30% more for foam board vs fiberglass batts which are very cheap.
Awesome. I just love creative solutions…. Not sure if I could handle the mess, although for $3000 savings…Maybe I could. \\ I need R-30 in my cathedral ceiling but I have 2×10 rafters…so I’m using R-30 mineral wool (supposed to be 7.5″ thick so will be able to leave a couple of inches for ventilation above.
I’ve got to say that this can not possibly be cheaper than spray foam. No way, no how. What is YOUR labor worth? I have a friend that changes his own oil because he says it saves him money. My response was always why are you having trouble making money. On to the engineering: There is no way anyday that this will not condensate. You now have a “mostly” insulated home with heat and cold still going about. Seems like major problems are in your future. Good luck.
what a load of crap. code requires R30? what a scam. how did people live before foam or any insulation, i guess they all just died? this is suppose to be the land of the free. life, liberty and the pursuit of happiness. this means you should be able to do whatever u want as long a u don’t impose yourself onto others. u want to build a house or buy a house with no insulation, that should be ur choice.
I did something very similar. In place of the foam board you used, I used 2″ Super Tuff R which I was easily able to cut with my leatherman knife. I also ran the insulation from the bottom of the floor joists joining the other side following the horizontal ceiling. I put 2 layers of the Super Tuff R in and over the walls at each end. It is now like one big refrigerator. This guy is losing out on air sealing by not doing the hole envelope. I also did not see the need to seal every layer. I only sealed to outer layer.
Holy crap what a savings. Well worth the effort I’d say. I had no idea spray foam was so expensive. Whomever occupies that room will appreciate it because without that insulation it would be a sauna up there. I have a similar attic room and I actually tacked up on the ceiling this foil radiant barrier they sell at Home Depot. It’s quilted with an air pocket built in and made a huge difference. Then I screwed down a grid of those 1×2 wood battens on top of the foil blanket and tacked on cedar planks for a cedar ceiling, so there’s an air gap between the foil and the cedar ceiling. Must have dropped the room temperature down by 10 degrees or more.
I cut the poly iso with a knife. You were probably faster with the cuts, but I had zero dust or clean – up time I will stick with a knife If I was doing 3 layers, I would have removed all the framing except for some strategic mounting points, then put the framing back afterward, the way you did it means tons of cutting insulation, and leaves you with no edges to mount drywall.
I did this 25 years ago except my foam was 3 in and foil faced instead of glass. Cut it with an extended large snap off utility knife blade. No dust at all. Bought my foam from a local shoring supplier. They go through tons of it building bridges and commercial foundations. Paid less than half what I would from a big box.
Wonder what the negative chemical equation is for hard foam vs spray foam. You would think most of the bad chems are staying in the attic and not being pulled down, but not sure. Also when I cut foam, I pull out the dust with a big vac, by just letting the vac stay on for about 5 min with hose hanging somewhere high and the air looks pretty clear, or you can blow it out by leaving a small salamander blower on for a few minutes. That dust is a bummer.
Super nice Job. The only thing I would have improved on was to put something in from the eve to the peak and keep your air space at 1-1/2 all the way up under the complete span of the rafter. This then helps keep a dead air space in the other areas and you don’t get any air washing going on. The industry works so hard to air seal the vertical walls, but ignore the ceiling area for some reason.
Do your cuts in front of an open window, with a cheap box fan or 2 blowing out, to avoid all that dust in the air. Sawdust and drywall dust both cause mesothelioma, same type of lung cancer as asbestos. I wouldn’t take chances with breathing that foam dust in a closed space. Do as many cuts as you can outside. Its worth a few trips up and down the stairs 👍
Hello Dave! I’m doing a very similar project in my 1950’s style home that has slopped ceilings but no insulation and no attic. Similar to the project in your article. I see you left the 1″ air gap. Does that air gap need to vent from the outside? I was thinking about leaving a 1″ airgap and also drilling 2″ holes into the eves to allow air flow to enter from the outside of the house. Is that necessary??? Am I doing more work than I need to??? Just worried about moisture build up and that creating mold. I plan to use Roxwool R15 or RAMAX Thermosheath 3 3-1/2″ thick insulation. Please advise. Thank you.
I do believe they call this the cut and cobble method I have heard that there can be issues with separation over time from the wood to the sprayfoam, I sure hope not because i did this in some areas of my home. I would have probably used xps as it is the best material on the market today. Nice work though, Im in an r50 zone, so this wont cut it for me.