Thermal Bridging

murbancz

What is the best way to prevent thermal bridging on a new home? Our village where we plan to build our new home requires, "The entire exterior must have a minimum of 1/2" OSB sheathing or plywood."

From my understanding they use 1/2" - 2" rigid foam board.

Can the foam board be placed on the exterior of the OSB and get the same results? I've heard of people having it placed on the interior side then using drywall over it. I would believe this would be more work for the electricians. Which by the way we need conduit. Also I can forsee problems with trim and base board.

Any help is greatfully appreciated.

Mike

concretemasonry

Get rid of the studs (thermal "short circuits") and don't pay a great deal of attention to the pink panther's old fashioned static short term lab tests that are used for product identification and advertising to fool everyone into thinking a R-19 insulation will give you a R-19 wall (which will be between R-11 and R16 even with the old concepts).

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Dick

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murbancz

So do you suggest using the concrete forms? I have heard that you have to be careful with getting the concrete to settle the right way in the forms. We want to build a 2-story home.

What do you recommend? What type of questions should I ask contractors when we are ready to build? What should we be looking for?

Thanks for the response.

naptown CR

you can use either SIPS or icf construction. another tack is to double frame the walls and leave a gap between inner and outer and insulate.

concretemasonry

First you have to plan ahead and do not make any last minute changes without looking at the situation "globally", which is not the local contractors/suppliers, but products, designs and materials plus what the majority of the developed/advanced world has already discovered. - Definitely not hay bales!

Second concrete does not "settle" as amateurs think. It is placed (not poured) and vibrated into place to maximize the benefits.

I was not promoting concrete construction, but pointing out how amateurish, short sighted and provincial the current "green" systems can be, especially when you follow the energy trail back and the total cost and carbon footprint can be if you have a short life structure and the associated recycling costs. It takes money, labor and energy to rebuild.

In Brazil (the home of wood) they routinely build masonry apartments using better local materials at a lower cost and they last longer and do not require the maintenance.

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Dick

Engineer, designer and consultant recently active domestically and internationally on construction and design in about 35 countries.

murbancz

Dick, what other type of products can you recommend? I'm not quite following you.

Naptown, thanks for the response. I was looking into the icf. I'm a little nervous about it.

Mike Hay

I.C.F is a great alternative to traditional stick built housing. With everything there are possitives and negatives. I.C.F is a very well sealed home that is so solid. If you live in an area that experiences earthquakes, these are the way to go. The styrofoam offers an r-24 plus the r value of the concrete and drywall. As for the concrete, I.C.F calls for a finer gravel crush so as not to get caught up in the rebar and create a hollow spot. Yes you can build 2 story in I.C.F, and as far as ensuring no trouble spots, you actually go around the forms several times using a concrete crane. So, do the basement in a pour, then add your floor, stack the main floor, pour it, and stack another level, and pour again. The draw back of I.C.F is really just in cost. Its a little more then traditional framing, and the trades you select should be ones familiar with working on I.C.F. They may also charge a little more as well. The ceiling of the home will still need a standard truss package that will require the attic insulated as normal.

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ESSaustin

To answer your original question, Mike: yes, placing rigid insulation board over the exterior of the ply will create a thermal bridge.

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ESSaustin

Oops! Just saw the posting date of the original thread...

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rustyjames

That's not what the building scientists are saying

SLSTech

Another oops - you forgot a word at least...

Thermal bridging is blocked, reduced, or eliminated when you use the foam as described above depending on temp. differences from the inside to outside - aka Delta T

Thermal bridging is basically referring to the heat transfer through the studs --- drywall - stud - exterior sheathing

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