Getting R-30 in an attic suite with 2x6 ceiling rafters 

This is a good book. Does provide a step by step introduction to how to build things ru-vid.comUgkxhgbP-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.

Pretty ingenious. And I like how you left the all important gap between the roof decking and foam. And the third layer of foam stops the thermal bridging.

TIP for working with insulation and fiberglass or polycarbonate translucent/transparent panels: Reverse your saw blade. It still cuts like butter through the materials but it does not kick out so much stuff all over the place.

I like how the 3rd layer covers the roof rafters, makes it a little harder on the drywall hanger but it does save a lot of energy. It's amazing just how much energy you lose from wooden studs.

Bosch T313AW3 jig saw blade is designed to cut foam and will do so with little or no dust. 3 blades for $15 on Amazon.

hint for working with fibreglass. stay as cool as possible, and don't sweat. if this means planning your work for cool days, do so!!! Take a full, cool shower immediately after working, THEN heat yourself back up after you're fully scrubbed with the cold water. This helps BIG TIME for the itchiness.

Your video 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.

That’s exactly the idea I’ve been batting around in my head for years. Thanks for the vid.

Polyiso foam cuts easily using a snap-off knife extended. Usually 2 passes with the knife will cut the foam cleanly. Plus this is quiet and no foam flying everywhere.

Thank you!! I’m a bit of a DIYer - redoing a master bedroom in a bungalow up in MA - 4x6 rafters. I was going to go closed cell spray foam because I didn’t want to lose headspace, but it’s so $$$! This video 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!

I had the same issue. We need only 1" of air gap above the insulation here in CA. Sister 1x2's to the rafters to give yourself 8" of space. Then take two layers of r-15, which will be 7" thick. Install normally. Prego.

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 video. 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 :)

Because the portion of the wall is sloped, in Canada, it's considered a wall, as far as R-Value requirements. However, an air space of 2 1/2 inch is required. This is required to prevent choking air circulation between other compartments.

Forget the worm drive or hand saw. Us an electric Turkey carving knife. Works awesome!! Thanks for the video.

Looks good; depending on how how hot your summer gets; a 10" auto shutter fan on one or both ends of the ridge would be a good addition; I had ridge vents across the entire length; and the heat still hangs without any prime mover. Peace

I have never heard of a building inspector forcing r30 for a remodel on existing construction... New additions, yes but if it was legal when built, they can't force you to upgrade it.

I'm in commercial roofing and very familiar with this material. Only thing I would have changed would have been to Isolate the air cavity with poly film. The facer of this insulation is organic and depending on location could result in unanticipated condensation and mold growth potential.

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. www.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 ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-Z292iuV91hA.html

UPDATE!! How's the foam doing 3 years later??? We send an endoscope up the air gap. Check it out here: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-5oSQhPvCvz0.html

I use a big shop vac hooked to the table saw for all my long rips. It cuts down on the foam board dust. Lots of dust like you show.

Radiant barrier on the top layer would have been a great idea.

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.

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.

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 50x50 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.

I just went through this. Building code approved all insulation installed and within 3 months everything weaped and condensates so bad it would have rotted off the roof in less than a couple years. It had full R and air space and still failed. Spray foam, spray foam, spray foam. Worth every cent.

I have seen foam insulation being cut with a hot wire on jobs. No idea about particulars (what types appropriate). Would be much less dusty

To cut without a mess, box cutter score both sides and snap. Or box cutter for the facing and a hot wire cutter for the foam

Cant thank you enough for posting this. I'm considering a diy for my attic and the visual of your thought process is enormously helpful. Thanks dude!

Maybe cheap in 2018, but here in 2020 2" foam boar is pushing almost $30 a sheet. It will take me well over $1000 just in foam board for a little bonus room.

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 2x10 rafters, so my R value was over 50. FWIW, a table saw works well to cut the material.

Looks like a toasty warm attic now, and for less money than spray foam! TY carpenter.

Polyioscyanurate is know to experience thermal value drift. Within a year of install, you are closer to R 28. If you choose to follow a path like this, shoot a bit higher than the code value so that you meet your performance target after the drift.

should have put some reflective foil on the top layer to reflect the radiant heat coming in from the sun....

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.

You can easily cut most foam insulation board with a 6" drywall taping knife and straight edge to almost eliminate the dust...

Genius! I just purchased an old home with 2x6 rafters, and someone back in the 70s or 80s hung fiberglass insulation right against the boards that the shingles are attached to (on the underside obviously). I’ll have to rip that stuff down, but I’ll give this method a try. THANKS!

You can use a Stinger cap nailer with 2” cap nail coils to make quick work of attaching the last layer of iso insulation to rafters.

Have done similar - but with Festool TS55 hooked up to shop vac - absolutely minimum dust and super accurate cuts leaving only the awkward fitment requiring ‘filling’ the fit was so good that I could only press the insulation boards home slowly as had to allow the air pressure to dissipate.😀👍

This is old but a layer of radiant barrier on the underside of that insulation with an inch of air gap would make a HUGE difference.

We use inch and a half polyiso on our rim joists with 2X4 compression blocking under stud centers to nail the belly board to. I use a wallboarder's Buddy drywall cutter for the polyiso. Score both sides and snap. No dust floating around in the air. It is really accurate and straight

I understand you need a channel between the rafters from the soffits to the ridge vent. But do you have intake vents at the soffits themselves, or just need an air channel between insulation and shingles so they can breathe (in effect just allowing airflow from the ridge vent)?

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.

I had the idea of doing this. You’re the first video i’ve Found on it!

Forget the space, with foam just go direct contact with the roof. If your inspector doesn't understand, ask him to show the code. Spray foam is direct contact, and well fitted sealed foam panels is to. Ventilation is way overhyped. especially in the north east.

The technique is interesting and it gives an air-break for the framing lumber which is good. The thing I don't understand is why do so much work to avoid a larger rafter. Just make it 2 x 10 rafters and avoid all of the finishing issues of the foamboard on the interior ceilings?

I love GRK screws! Expensive, but well worth the cost!

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.

Get a couple 20 in box fans and a couple cheap 20x20 air filters and duct tape the air filters to the intake side of the box fan. Constantly filters the air... I'd still wear a mask bro!

I cut 2" foilfaced foamboard with a razor just like drywall, it's quicker and if you razor it well it breaks very evenly.

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.

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 1x2 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.

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.

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.

Wow! I scanned the comments and found I already saw this..... I have officially watched every video on RU-vid and am starting again! This video is a great place to start! tHanks for the video!

you can cut any foam insulation board with a long box cutting knife, no dust if done that way. just score it a few times.

Nice Work. Thank you for reaching out to help others !

You can tape a vacuum hose to the back of the saw

The r value requirements in building are only to support traditional insulation in a laboratory setting. The vapor and air barriers alone in spray foam mean you can use a tenth of the depth and achieve MUCH better results

I usually fir the rafters 2” down for this exact reason. Good solution either way.

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.

I ground all the teeth off a 10” blade so it has a knife edge. I cut lots of styrofoam installation with that blade in my table saw with little or no dust or styrofoam chips.

Hey, you don’t need an air gap on roof framing bays that are filled solid with rigid foam insulation! Company’s that blow on expanding foam fill the cavity solid, it’s the same concept.

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

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.

Decent job. Still didn't get R30 in that 2x6 area. You had to go to the outside. I would not put R13 fiberglass on those knee walls and fiberglass R30 on flat ceiling after all that work on the slopes. Finish the job with the foam boards.

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.

There are 4.5" polyiso panels that insulate to R30. I'm thinking of trying those instead to cut down on the work, rabbeting the edges to give 1.5" over the rafters for mounting and leaving an air gap.

1) Could you do most of the cuts outside, at least all the repetitive standard dimensions? Leave the dust there instead of in the attic? 2) Could you cut it with a hot wire cutter so you would not create all the dust in the first place?

You could also have installed R22 roxul batt (5.5inch) by adding a 2x2 over your 2x6 with an R10 of ridgid insulation (like Dow Cladmate) with strapping and drywall (add maybe R2) that give you around R34. Three big advantages: faster, a little bit cheaper and better sound insulation.

they do make roxul 2x6 in r24 its super dense and hard to work with

I'm in Canada, and those sheets come in 4'x8'x2" for $48.00! Also, building code may require the addition of a non-flammable surface in the room (dry wall), as the surface it comes with may not be accepted - definitely needed for 'bare' foam boards, of spray foam.

How did you attach the drywall to the slanted walls, given the thickness of the insulation?

Thanks for all the detail! Many vids will tell you some and show nothing. Awesome job!

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.

Polyisocyanurate is R6 for each inch. And you should get foiled. Its also just easy to use a can of spray foam to make mound of space instead of cutting wood, gluing wood, and so on. Just spray a dot of spray foam in a couple corners and you're done. That black backing is made so you can cut the foam slightly smaller so you have about an inch or 2 of the paper you can simply staple down vs the washer screws.

Bet that drywall guy didn't like that crap one bit! Kinda sketchy not having the sheetrock fastened to the rafters! This is just looking for trouble in the future with expansion and contraction.

You could have had 4 inches of closed cell foam blown in for the same price with no labor and had air sealing and added structural integrity.

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.

Countersunk screws work nicely with fender/repair/penny washers and sit flush. An insulation saw with teeth like a bread knife makes less powder. Foil faced PIR insulation gives a built in vapour barrier. Foam fill any gaps and cover all joints with aluminium tape.

Hey Dave, so when you added the drywall you simply used longer screws to overcome the foam? Thanks.

Forgot to add that the 3rd layer at 90 degrees is great for making a thermal break for the wood rafters. Wood is just a moderate insulator.

LOVE the rain on the roof. Great place to sleep.

You only have to fur out the area that's insulated... I'm a framing Carpenter you can always build knee walls to get the rafters higher but we use a lot of 2x8 and 2x10 rafters here....

Timber framers that use 6"-8" thick roof panels don't have a air space?

I wish I could have done that to my house. My 2x6 rafters are not accessible accept through a tiny crawl space. Your project looks great though.

"hot roof" look it up, no ventilation required BUT closed cell spray foam needed to stop moisture vapor flow. I use it in Michigan where R50 is required. Works so well the snow sticks on a 12-12 pitch roof. Yes it is code.

Almost all major shingle makers allow for a unvetted roof using closed cell foam that is at least 1.5-2". Also XPS foam you can score and snap with no mess

Just know polyiso is very flammable. Rockwool is non flammable, water doesn’t absorb into it so it doesn’t mold, and critters and rodents hate it.

Grk screws are super expensive

There are band saw blades that don't have teeth (a knife effectively) used for cutting stuff like that. There are probably similar blades for reciprocating saws, or make one.

The logic here for insulation is well thought and presented. However, in case of a fire, this is horrendous. Stay safe out there.

You dont need ventilation if your insulating directly to the roof deck. You can get R30 with 2 layers of 2.6

My carpentry teacher says roof raftering will be coming back (in canada). Too much wasted space having attic, with negligible insulating values. Engineers and builders just like to keep it simple with engineered trusses.

What if there’s no ridge vent, or soffit vent either? I’ve got a garage with similar plank roofing and only 2x4 rafters. Wondering if it makes sense to have that 1-1/2” air gap if there’s nowhere for the air to vent out

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.

How are you planning on attaching drywall to that now?

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 video to explain how this works....

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..

Yeah those guys doing spray foam has drove the price unaffordable for most people it’s ridiculous. They’re pricing themselves out of business