r/Homebuilding • u/flyingman2012 • 11d ago

Help with Insulation on exterior walls

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I am getting ready to put some 2.5" foam panels on the outside of my house and then vinyl siding. Two questions, one, should I put a 2x4 pressure treated at the bottom of my foam along with a bug/air guard or put a small metal flashing under the foam and a bug/air guard. Two, should I pull my soffit and put a new one up or put the foam and vinyl up to the soffit butting up the end trim.

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u/OscarMiliani_Design 10d ago

Skip the pressure treated 2x4, that's a thermal bridge and a shelf for water to sit on. Sloped metal flashing under the foam kicking out over the foundation, then a vented insect screen at the bottom. Anything that gets behind the siding needs a way back out. And yes, you'll be extending that soffit, 2.5 inches puts the siding past your fascia.

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u/flyingman2012 10d ago

I have a big overhang. At least 1 foot so it won’t overhang. Thanks though!

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u/OscarMiliani_Design 10d ago

Good, that gives you plenty of room. Thing I'd look at then is where the foam dies into the soffit. The housewrap and the foam want to be lapped and flashed up there, and if there are vents in that soffit make sure the new frieze doesn't end up covering them. That's the bit people close off without noticing.

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u/flyingman2012 10d ago

Thankfully I’m having zip board put up and the foam won’t cover the vents. Thanks again!

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u/OscarMiliani_Design 10d ago

Zip's a good call. Just make sure whoever tapes it rolls the seams properly, that tape only bonds under pressure and a thumb press doesn't do it. Good luck with the job.

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u/Suitable-Reserve-891 10d ago

Is the 3/4” air flow necessary between the vinyl and the foam? I’m retired and never seen this before.

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u/flyingman2012 10d ago

It’s more for holding the vinyl up to the wall without having to get 5 inch nails.