I am trying to build a conventional stick built house and making it fairly air tight without breaking the budget. Hiring a contractor to come in and spray foam everywhere is not a choice I can afford.
The house is framed, sheathed, and roofed. The windows are in, and the exterior doors will probably be in place tomorrow.
The walls were fairly easy to seal up, and with a few tubes of caulk and a couple of cans of spray foam, they will be in really good shape. I used a peel and stick roofing membrane as a house wrap and flashing for the doors and windows. 4×8 sheets of polyiso foam on the outside of the roofing membrane, and the insulation is done as well.
Cost effective air sealing the ceiling at the sheet rock level is the next challenge. I plan on blowing in about 16″ of cellulose which should go quite a ways towards reducing infiltration, but I really want to improve on that if I can do it at a reasonable cost. I’m looking at several possibilities and may use a combination.
One wild idea is to use the foam sill sealer strips as a gasket between the sheetrock and the top plates.
Another approach is, once the sheet rock is in place, a foam gun, a case of gun foam, and a few hours sealing every top plate to sheet rock joint I can get to. The roof is a 6/12 pitch, so some of the outside walls are going to be really hard to reach.
Going up in price, three grand worth of Tiger foam, and 1″ of foam over the whole ceiling – starting to get out of the cost effective approach though.
Any other wild ideas floating around out there?
Replies
You might try doing a seach of the FHB archives for an article on air tight drywall construction. Seems like it was 10-15 years ago, maybe longer.
Dave
Paul, I know a builder in Denton who may give you some advice
He is building affordable high performance homes
He uses the air sealed drywall approach to "enclose the air"
He may have some local advice. His name is Dan Fette and the project name is Nevada Court..let me know if you need his phone #
And thanks for pointing me to Ray Moore
John
We've used the sill sealer on the top plates for years. drive four utility knife blades into the end of a 2x6 and pull the sill sealer through it into a trash can to make 1 1/4" foam tape. Staple it up on the lower of the two top plates both interior and exterior. takes about three hours with a slap tacker and your done. The sheet rockers work with us (and we with them) by waiting for the ceiling to be hung and then stapling up the foam before they hang the walls. It's called "the air tight drywall approach" and there is plenty of data and experience on it out there.
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"You cannot work hard enough to make up for a sloppy estimate."
ShelterNerd,
learned something new from you again !
You should post a photo at your site. But it sounds so simple that maybe a photo is not needed. Do you have any other tips on "ATDrywall"?
It may be easy to find people in North Carolina that are doin this stuff... but I have found it difficult in North Texas.
John B
Thanks for the tip!
"foam tape to the lower of the two top plates"
Do you then use drywall adhesive on the upper plate?
I also found some decent information at
http://oikos.com/library/airsealing/index.html
Can you further explain this air sealing at the top plate to the drywall?
If I understand, you have foam tape horizontally on the lower plate of the double top plate of the walls?
If you drywall tape and spackle the corners at the wall/ceiling and wall/wall corners, how/why does the foam do anything more?
Priming properly with PVA and then a proper painting of the drywall should prevent any leakage from inside to outside.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Phil,I'll jump in here. I've always been a little unclear myself on the wall/clg leakage. But as I understand it, air leaks into the wall through electrical outlets, under baseboards and such. Then if the wall sheetrock is not sealed tight to the top plate, it can leak between the sheetrock and top plates, behind the wall/clg corner and into the space above.A few years ago one of the guys on here was promoting delaying framing of the interior partitions till after the ceiling was sheetrocked so you would have a monolithic lid. Not sure how practical that would be in the real world...Steve
Maybe the plate sealing at the ceiling (!!!!) might add something to all the measures collectively. However, *you're* supposed to seal around the outlet/switch boxes, and use flexible caulk at the floor and drywall joint.
Although I haven't seen the foam tape used at the top plate, wouldn't it cause the wall/ceiling corner to NOT be exactly square ?
As to drywall before partitions...... it can be done if you are both the framer and the drywaller. The aim is also to rock the exterior walls before the interior partitions (non-load bearing)
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
MMoogie has it right. Go up in an attic of an old house and you'll see staining on the insulation over the walls from air running up through the walls and leaking between the top plates and the back of the drywall into the attic. This idea originated with Joe Lstiburek and the work he did back in the 70's or 80's in Canada with the Canadian R-2000 program AKA the "air tight drywall approach". It's an inexpensive thing to do. just take a 2x6 about 16" long and drive some 16's in the edges to make a runway for your sill seal. Then drive some utility knife blades into one end about an inch apart from each other and tack it all down to a work bench or saw horse with an empty trash can next to it. Pull the 6" sill seal down the track and through the blades and drop the resultant foam spaghetti into the trash can. Now run around and staple the foam to the top plates interior and exterior. If you can wait until the rockers have hung the ceiling and get in and do it before they hang the walls it works better. Thats not always practical. (the attached photo shows it done before the rockers hung the ceiling.) This seals the top of the walls from the attic and improves performance in a home that is insulated with fiberglass. It is not needed in a house that has a spray foamed (conditioned) attic or in a room that does not have unheated attic over it such as the first floor of a two story home. Hope this helps, the house in the photo hit 49% better than code on the energy star evaluation. Not bad for fiberglass insulation and no active solar...------------------
"You cannot work hard enough to make up for a sloppy estimate."
Well, if the air sealing around the outlets/switches, air sealing at any wire holes etc, and caulking at the floor are done right, then nothing will be able to get to top plate from inside the wall. Plus densepack or wet spray cellulose and you really do not need that foam strip IMHO.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
I think the foam is cheaper and faster than air sealing the switch and outlet covers and caulking the drywall to the floor. You still need to air seal all the wiring and plumbing penetrations. And I think you will find that even dense pack or wet spray cellulose is not an air barrier. I thought I built a good house. and then I joined energy star and started blower door testing and duct blaster testing every house I build. I've improved a whole lot since I started testing, and I've gotten better on indoor air quality at the same time.------------------
"You cannot work hard enough to make up for a sloppy estimate."
Well, there are air barriers and there are air barriers. Depends on the conditions. Cellulose is not an air barrier if the air is under heavy pressure, but it will block airflow of ordinary conditions of a house wall or attic. And much better at it than fiberglass batts at any pressure. Fiberglass was designed as an filter media.
We're getting a bit off topic.... I dont want to relive the cellulose wars.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
Fair enough, I'm a spray foam guy these days anyway, no dog in that hunt.M------------------
"You cannot work hard enough to make up for a sloppy estimate."
Phil,Air sealing of outlet boxes and floor plates should help, but how often do you see that happening on interior walls?I too am a fan of both spray foam and DP cellulose. I like getting a monolithic thermal perimeter. I don't like to have to rely on caulks and sealants.I would like to start doing some blower door testing. Would be very interesting.Steve
I guess it all depends on how the air sealing is attained, even on interior walls.
Quantum materiae materietur marmota monax si marmota monax materiam possit materiari?
The jig for cutting the sill seal into strips works very quickly. In my case, 2,230 sq. ft. house, equals 5 rolls of the 6" sill seal and about 3 boxes of staples. My hammer stapler seemed to be the best choice for attaching the stuff.I will also seal all the electrical boxes, etc. It's my house, and I am going to seal it as well as I can.
Have any of you had experince with regular code compliant vapour barrier in Canada? All electrical boxes on the outside walls are sealed (with a vapour boot or sealed plastic boxes). We use 6 mil rated poly for a vapour barrier (the paper faced batts are a joke!). We use plate poly between the top plates on the walls, and between the interior and exterior walls. This allows a good sealing surface for the vapour barrier. All joins in the vapour barrier are tuck taped or sealed with acoustical seal. All joins between the vapour barrier and framing are sealed with acoustical seal. (for example there is a heathly bead of acoustically seal laid down between the floor sheathing and the bottom plate, then the poly is laid into the bead.All penetrations through the vapour barrier are sealed (we use acoustical seal mostly, especially around vent pipe going through the top plates to the attic.Properly applied, when the vapour barrier is complete, the house is sealed. You will have a hard time slamming an outside door because it will bounce against the trapped air! (if all the windows are locked shut). It doesn't really add to the insulation costs too much, and it probably adds 8 hours to the insulation labour. The average house will require about 30 tubes of small acoustical seal, 5 rolls of tuck tape, 5000 staples (T50 or JT21).The methods discussed here seem stop gap. Why mess around with all this when you can do it right from the start?
different climate, different answers.
A sealed vapour barrier is the ideal answer for Canada.
It is a sure recipe for disaster in Texas.
the house in the photo hit 49% better than code on the energy star evaluation. Not bad for fiberglass insulation and no active solar...
Michael,
I totally agree with a need for energy star, projected performance numbers and testing.
I am curious as to how your homes are perfoming in real life compared to the projected performance. Did the fiberglass project meet the evaluation?
Our raters do not seem to allow a great distinction between fiberglass and spray foam...yet I feel sure that the foam is superior.
Have you had any big surprises in performance vs. projected on other projects?
I know you can not change the habits of the homeowners..but I can imagine that some owners could throw a wrench into the mix.
John
Try combining two insulation methods. Get a quote from a spray foam insulator to apply no more than 1" of material, then install fiberglass. This is a very effective hybrid technique. Good Luck Jay
The spray foam is about a $ per board foot, so one inch of foam over the whole attic would cost about $2,300
The total cost for R49 cellulose is $1,200. The spray foam does not seem all that cost effective.
The spray foam does not seem all that cost effective
Which is true, if you insulate the ceiling.
If, instead, you make the insulation plane follow up the wall to the bottom of the roof deck, you wind up with a conditioned attic instead. Roof plane is often much, much easier to seal than the ceiling.
Ok, you will likely "break" 3 grand for the additional area of foam, but you get to run your hvac system in 80-90º temps instead of 130-140º temps (in winter, the attic will run in the 70s instead of 40-60s).
You do gain the additional "headache" of having to insure that all of those "leaky" things (vent fans, especially) actually move water vapor outside of the envelope, and not just dump it in the attic where the roof ventilation will (supposedly) take care of it.Occupational hazard of my occupation not being around (sorry Bubba)
The roof plane would be a LOT easier to seal than the ceiling.
However, my roof plane includes 600 sq. ft. of porches, and also extends over the breezeway and on to the garage. So, insulating at the roof plane would involve sealing off the attic above the two porches and the breezeway from the conditioned part of the house - which decreases the size of the roof plane needing insulation, but increases internal walls in the attic that would need to be foamed.
If my HVAC system was going to be in the attic, I would figure out some way to do it anyway. However, the HVAC is all in a nice cool conditioned crawl space with concrete floors and a 7 foot ceiling. It is being installed today in fact. It is a whole lot cooler down there than it is up in the house proper.
The vent fans are inline fans also located in the crawl space, and their exit is through the walls. Sealing around them is going to be relatively simple. The attic will have some wiring and insulation. Nothing else. The only holes in my roof are the ridge vent and some plumbing vents.