Continous foam insulation on the inside or the outside of the wall?

Golden view · Feb 2, 2017

I know Thorsten a bit, was a much bigger builder than me in Alaska. He built some interesting homes. One had a 5000 gallon heat storage tank and 24" thick walls. R100 lid. Plywood before drywall to hold up the insulation.

Rio · Feb 15, 2017

So we've been reading up on working with continuous foam insulation on the exterior, how to install windows in that type of wall assembly and how to attach various types of cladding and came across this detail for attaching a window at the inside of the foam.

I have a concern with this detail but I'm not sure if there's anything to worry about so I thought I'd check here and hopefully get an answer to my question. The question is: Is it okay with the self-adhesive flashing that is wrapping the outside corners of the foam to be reversed flashed at the head of the rough window opening?

We've always been taught to 'think like a raindrop' and never do any sort of reverse lapping. My concern is the adhesive might dry out or the flashing might wrinkle and then be channeling water behind it and over the top of the window frame.

Is the self-adhesive flashing so sticky that it essentially is welded permanently to the foam or is this a valid concern?

Thanks for any insight on this!

Philament · Feb 15, 2017

That photo is for a double stud wall with insulated header and zip sheathing, not the best example of of innie window flashing details as a general course.

That specific example is using the tape as a continuity of air barrier, not necessarily flashing, the extended frieze board is acting as a psuedo drip cap. Usually the the head flashing is a 3 part thing, where you air seal the opening, then you add your drip cap into a reglet in the foam and tape the seam.

As for the tapes....all tapes are not created equal. I will falsh my openings with a butyl tape (dupont flex wrap, blue skin, grace vycor...etc), because they are flexible and come in sizes that can span the opening to maintain continuity of the air barrier. Unfortunately butyl tapes have a tendency to "fish mouth" over time, especially the head section. Therefore I seal the edges of the butyl tape with acrylic tape, which is much more tenacious in bonding long term. For directly to foam though, there are different tapes for that. My preference is siga Wigluv or Siga fentrim, but owens corning, dow, and 3m make their own versions that are specifically for sealing to foam and can be used as a "weld" (for lack of a better term). Foam expands and contracts a fair amount, so the tapes not only need to stick to the foam, but be able to take the stretching as well.
Zip uses a different type of tape, they have a flexible acrylic tape for flashing windows and pressure sensitive acrylic seaming tape. Kind of similar to Nichigo G-Tape.

The flashing/taping question really depends on what and where your wrb is. If you're using house wrap over or under the foam, then you'll be sealing to it. You can use the foam as a wrb, but make sure to use the manufacturer's recommend seaming tape for that application.

Philament · Feb 15, 2017

This is a better example of an innie window flashing where you can see the multi-tiered flashing where the wrb is behind the foam. The one detail that isn't terribly well explained in this example is that the horizontal furring strip behind the window trim should be venting, either by kerf cuts, cap nails, or using a product like coravent, to let air in behind the siding and allow any condensation to drain out.

It seems like all of the examples I find use flanged windows, but I prefer not to use them because they're virtually impossible to change out without tearing the whole wall off.

Here's an example of what I mean by taping the butyl flashing tape with a secondary tape to prevent fishmouthing and adhere to the foam (Dow Weathermate in this case).

ScipioAfricanus · Feb 15, 2017

Hey Rio, there are some other things that can be done that do not involve the walls with EIFS and such.

Putting spray insulation in the rafters for example and thereby having the HVAC inside the conditioned envelope etc.

Would need to know the overall of the project, though.

Andy.

Rio · Feb 16, 2017

Thanks so much for the good information Philament! The detail explain a lot and the photos clearly show the double taping. I haven't been exposed to any of these newer techniques and need to get up to speed on what is involved and the best way to deal with using these continuous foam insulation products.

Scipio, what I'm looking for right now is general information on the subject. As I'm sure you're well aware of being a designer here in Cali, the new Title 24 part 6 energy code cycle is here and the default wall assembly has the continuous foam as part of it. This is making it really hard to get projects to comply without using the foam.

As a result I want to be able to have a library of valid construction details for all parts of the wall assemblies, for my own use if needed and to share when doing energy calculations and reports for clients. Down here by the beach we can still skate on having to use the foam but once we go inland into a harsher climate zone we've been warned that it's going to be almost impossible to get a project to comply with using continuous foam.

SLSTech · Feb 16, 2017

Sorry just saw this & there is a ton of good advice on here. I would suggest reading up on the "perfect wall" by building science corp for more details, etc... As for concerns about holding power for cladding weight, etc... many manufacturers have details for just that as many parts of the country/continent have been using exterior foam board for a while

As for interior, that is generally only for retrofit options in older historic homes & inside basements where adding it on the exterior would be a nightmare

Fouthgeneration · Feb 17, 2017

I think we are seeing an home design evolutionary dead end caused by the artificially high energy prices caused by the current Anti-Carbon Mania. Electricity and other forms of Energy will shortly return to getting ever cheaper as all commodities do in a rational ever growing economy....

A Few linear equations will show the windows and doors have a much greater effect on the heat loss/gain of a home envelope then an ever thicker wall...
Automated insulating shutters would save more than another 2 " of flammable blue board...& or internal automatic curtains....

One should consider the habitability of the house in a long term civil war or economic collapse.....Think inner city Chicago... or DC during the Crack years.

If your house is built in a land of fools like Californians living under un-maintained reservoir Damns, who cares what the power bill is?

ScipioAfricanus · Feb 17, 2017

Rio said:
Thanks so much for the good information Philament! The detail explain a lot and the photos clearly show the double taping. I haven't been exposed to any of these newer techniques and need to get up to speed on what is involved and the best way to deal with using these continuous foam insulation products.

Scipio, what I'm looking for right now is general information on the subject. As I'm sure you're well aware of being a designer here in Cali, the new Title 24 part 6 energy code cycle is here and the default wall assembly has the continuous foam as part of it. This is making it really hard to get projects to comply without using the foam.

As a result I want to be able to have a library of valid construction details for all parts of the wall assemblies, for my own use if needed and to share when doing energy calculations and reports for clients. Down here by the beach we can still skate on having to use the foam but once we go inland into a harsher climate zone we've been warned that it's going to be almost impossible to get a project to comply with using continuous foam.

I respect that and understand that you are looking at wall details, but as you know here in Calif. we have to take a more broad look at the entire structure when doing Title 24 part 6 energy analysis.
I have found as an energy consultant that the roof plays a much bigger role in energy savings than the walls and it is usually more economically sound to start at the roof portion of the thermal envelope before looking at the walls.
The next to consider is a tankless water heater then Quality Insulation Installation (QII) then the walls.

If one could put say, R-30 or R-38 in the roof rafters or put 2" of foam on the roof deck then R-19 in the rafters that opens up huge energy savings for all the rest of the parts of the envelope and energy analysis.

So much so that you could go with 2x4 with R-15 in the bays and no continuous insulation.

Andy.

Rio · Feb 17, 2017

Thanks for the good tips Andy, appreciate it. In the past for additions we've found changing from a tank type water heater to a tankless has been one of the 'silver bullets' in acheiving compliance with the energy regs.

Now in 2017 it's a different story, especially for new construction. For additions and alterations the only way one can get credit for the change is to get a HERS rater to certify the existing condition, otherwise no credit. For new construction the prescriptive condition is a tankless. In order to do a tank type one one must also do HERS verified QII (Quality Insulation Installation) and either HERS verified compact hot water distribution system or HERS verified DHW pipe insulation. One won't pick up any compliance points by using a tankless although one can by using one with a higher E.F. (Energy Factor).

A way to get compliance on alterations and additions without having to get too extreme is to use a HERS rater to verify existing conditions. If one has an existing attic with no insulation and gets that verified then when one puts in R-30 or R-38 one will get a huge bump in compliance points. This can be used for walls, windows and as mentioned above for water heating.

The other two big changes for the 2016 are the prescriptive wall and roof assemblies. I've put the link below to the summary sheets from Energy Code Ace regarding them. At the last seminar I went to on the subject, Martyn Dodd, who writes the software for Energy Pro, was saying that this iteration of the energy code is about 30% more restrictive than the 2013 code which was about 30% more restrictive than the 2008 code. That's a 60% increase in 6 years! By 2020 all new residential construction will have to be ZNE (Zero Net Energy).

By having these more extreme measures as the new default it is going to make it harder and harder to achieve compliance and it looks like the continuous insulation is going to be needed more and more.

Here's the link to the summary cheat.

http://energycodeace.com/download/8866/file_path/fieldList/...

Continous foam insulation on the inside or the outside of the wall?

Golden view

Rio

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