Thermal bridging

2511 Views 15 Replies 6 Participants Last post by Gary in WA, Jan 4, 2013

tornstrom

Discussion Starter · Jan 2, 2013

Hi,

I'm in the process of building a new house and I've been thinking about ways to get rid of the thermal bridging that the studs create.

One way to go would be to add a 1/2" rigid foam board before the drywall. This would be pretty simple to do and would create a continuous thermal break. I have seen this done and discussed and it appears to work well, however I'm concerned that it could create a condensation surface on the rigid foam.

The other way would be to strap the walls with 2x material at 16 or 24 cc and fill the cavities with 2" insulation. That would only create thermal bridging where the strapping crosses the studs. This would be more labor intensive but without the risk of condensation inside the wall.

Walls are framed with 2x4. Exterior is done, so any additional insulation has to go on the inside. This is in central Texas, so I'm mainly concerned with keeping the cold inside the home

Any ideas or comments on above approaches? Has anyone any experience on this matter? Is it even worth the effort?

Thanks

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Windows on Wash

· #2 · Jan 2, 2013

Rigid foam should always be on the outside wall and not the interior wall.

Where is the home located?

Interior foam will keep the studs even colder and further increase their chance of condensation.

Reactions: 1

tornstrom

Discussion Starter · #3 · Jan 2, 2013

Windows on Wash said:
Rigid foam should always be on the outside wall and not the interior wall.

Where is the home located?

Interior foam will keep the studs even colder and further increase their chance of condensation.

Austin, TX.
Yeah, it should be on the exterior but I've heard about people using it on the interior (some thread on contractortalk) and some of them seem to think it's a good idea.

The warm side would be the outside here in TX, so the foam would keep the studs warmer. I don't know where the condensation would take place in this case though.

Windows on Wash

· #4 · Jan 2, 2013

While the vapor retarded (if any) should be on the warm side, exterior foam still helps with vapor drive from the outside and helps keep the moisture out of the wall.

Depending on the foam, you may be eliminating the walls ability to dry to the inside and this could create issue.

What is the exterior of the home?

Reactions: 1

Maintenance 6

· #5 · Jan 2, 2013

I saw a house framed to eliminate thermal bridging. What the builder did was to use 2x8 top and bottom plates and built two 2x4 walls on 24" centers. One was framed on the inside and carried insulation and drywall. The other was framed to the outside and carried insulation, sheathing and siding. There were no holes drilled through the studs for wiring. The 24" centers were offset from each other by 12" and the corners were framed to stay independent inside to outside. Around window and door openings they cut the studs down to allow about a 1/2" gap between the walls and the headers were independent from eachother inside to outside. They used only a few small blocks to tie the walls together in those locations. I don't know how the energy calculations worked out against the construction costs, but in the end it was a super quiet home.

tornstrom

Discussion Starter · #6 · Jan 2, 2013

Windows on Wash said:
While the vapor retarded (if any) should be on the warm side, exterior foam still helps with vapor drive from the outside and helps keep the moisture out of the wall.

Depending on the foam, you may be eliminating the walls ability to dry to the inside and this could create issue.

What is the exterior of the home?

It's 3" brick veneer with 2" ventilated air space. I think I might be over doing it trying to get a thermal break.

tornstrom

Discussion Starter · #7 · Jan 2, 2013

Maintenance 6 said:
I saw a house framed to eliminate thermal bridging. What the builder did was to use 2x8 top and bottom plates and built two 2x4 walls on 24" centers. One was framed on the inside and carried insulation and drywall. The other was framed to the outside and carried insulation, sheathing and siding. There were no holes drilled through the studs for wiring. The 24" centers were offset from each other by 12" and the corners were framed to stay independent inside to outside. Around window and door openings they cut the studs down to allow about a 1/2" gap between the walls and the headers were independent from eachother inside to outside. They used only a few small blocks to tie the walls together in those locations. I don't know how the energy calculations worked out against the construction costs, but in the end it was a super quiet home.

I used this type of staggered studs in the utility room walls that connect the garage to the kitchen. I used 2x6 plates though, but I think it will reduce sound from washer/dryer and garage work by a lot! 2x8 plates would make it a lot easier to insulate.

woodworkbykirk

· #8 · Jan 2, 2013

its called a double stud wall

Reactions: 1

Windows on Wash

· #9 · Jan 2, 2013

Don't both with the foam. Double stud it if you really want the additional R-Value or put in SPF.

stadry

· #10 · Jan 2, 2013

anyone building a new home would be well advised to use icf's - the initial addl expense over std wood framing would be pd back w/i 18mos &, from then on, its all gravy,,,houses are extremely quiet, have very low hvac costs, & are more hurricane resistant :thumbup: typical wall rating is r-50 :yes: the last figures i saw said icf's have 20% of the new mkt,,, we built several structures of them & i'd use them for my own home ! ! !

woodworkbykirk

· #11 · Jan 3, 2013

your right about the drastic savings in heating costs for a icf however the cost recovery for paying hte extra isnt 18 months its about 5 years. there are other considerations that make rough ins for mechanical more difficult than in wood construction.

im a licensed installer for both nudura and arxx icf systems.
3 years ago i build a 4200 sq ft vet clinic that is icf construction.. the old old location for the clinic was only 950 sq ft in which the heating /cooling costs were about 3.5x greater for a 6 month period than the new space which is just over 4x larger

Windows on Wash

· #12 · Jan 3, 2013

I love the stuff and would love to get schooled up on it.

What do you two guys recommend?

tornstrom

Discussion Starter · #13 · Jan 3, 2013

Apparantly a product exists for thermal breaking of studs. http://thermablok.com/ Not sure what it costs, i bet $$$$.
Aerogel is an extremly bad conductor. I ordered a sample of this material many years ago and it was quite mind-blowing. Like solid gas

woodworkbykirk

· #14 · Jan 3, 2013

hey window. i responded to your pm.

as per icf products. nudura and integraspec are considered the two best products on the market. the big plus with integraspec is for commercial applications.. you can open the panel up after a wall is erected and get access to the plastic webs so you can change the rebar detail if needed without taking the wall down

there are a bunch of icf manufacturers now, however quite a few are horrible. the first one i ever used was from a roofing supplier.. the blocks wouldnt stay locked together on the horizontal joints so we had to glue them together with spray foam and use strapping to help lock it together.. ill never use that product again

stadry

· #15 · Jan 4, 2013

think our 1st supplier was a stand-alone subsiduary of reward - rep was a great guy ) later folded back into reward,,, it was our 1st gc job & the only reason we did it was the only local contractor ( nudura ) was outrageous in $$$,,, don't think we ever had a cleaner job-site compared to wood or cmu's,,, fastest & strongest bldg yet, too,,, our electrician took the work at t&m but, on the 2nd go-round, he dropped his $$$ as did our conc supplier & pumper - they liked 'em, too :yes:

Gary in WA

· #16 · Jan 4, 2013

What type of sheathing- OSB or plywood? Any block in that wall?; http://publicecodes.cyberregs.com/icod/irc/2009/icod_irc_2009_3_sec016_par015.htm

Gary
PS. You can also cut 1-1/2" wide strips of XPS for on the studs/plates before the drywall...ADA the drywall to limit air movement.

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