Community: Building Code Questions

Q & A Instructions

[Click map to enlarge]

The web site has a wealth of articles on a wide variety of construction topics. Before posting your question, you may want to check out the articles on this page: How To Do Everything. You just might discover an article there that provides the information you seek.

Please register for a free account or sign in to ask and answer green building questions.

If you want to post a question, the usual rules of courtesy apply:
1. Be nice.
2. If you can't be nice, be polite.
3. If you can't be nice or polite — well, please be brief.

To attach a photo or illustration: Under the box labeled “More explanation,” look for the words “File attachments.” Click that, and you should be able to attach a photo.

Thanks for joining the conversation!

3 Answers

Permanent wood foundation (PWF) backfill height?

All the documentation I've found on PWF basements never shows insulation under the slab floor. The allowed back fill heights are always referenced to the bottom of the bottom plate of the wall which coincidentally is the bottom of the slab.

If under slab insulation is installed after the perimeter PWF walls are in place, the slab will be raised by the thickness of the insulation. With under-slab insulation is the backfill height the height above the slab bottom? or the bottom of the bottom plate?

Asked By Jerry Liebler | Apr 17 17
3 Answers

Deck footers

Good evening Everyone,

I'm attempting to build my first deck this spring. I've dug holes for footings and just passed my footing inspection.

The Deck code here in maryland dictates that holes are to be a minimum of 30" deep with an 18" wide by 10" deep concrete footing. Once you have that you can either use concrete piers to get your posts out of the ground or you can place the post right on the original footing.

Asked By Andy Pappas | Apr 17 17
1 Answer

15 minute thermal barrier

I have had 3" of Bayseal Closed cell foam sprayed into the exterior walls of my cabin. My intention was to apply 3/4" interlocking car siding over the insulation but our building inspector is suggesting it does not satisfy the 15 minute thermal barrier required. Does anyone have any information on this? I could use 1/2" drywall over the top or spray with a retardant but I'd rather not. If I use a retardant, any suggestions?

Let me know


Asked By maggiebo | Apr 5 17
1 Answer

Exhaust vent outdoor opening size?

Okay, this is a nitpicking detail, but what does this part of the IRC mean?

R303.6 "Air exhaust and intake openings that terminate outdoors shall be protected with corrosion resistant screens, louvers, or grilles having an opening size of not less than 1/4" and a maximum opening size of 1/2", in any dimension."

Does this mean that the holes in an exhaust vent have to be smaller than an 1/2" circle? That doesn't line up with most of the vents that I've seen on the market, especially dryer vents.


Asked By John Ranson | Mar 27 17
10 Answers

Sealing PEX and PVC pipe penetrations

I am reposting this to the Code section; not getting an answer in General Questions.

What do I use to meet code-required fire blocking and good weatherizing/air sealing for the circumferential individual tube/pipe and ganged tubes (a cluster of tubes), penetration gaps for PEX-to-wood (and plywood) and PEX-to-PVC pipe, and for PVC-to-wood, and PVC- & PEX-to-drywall?

With manifold distribution and multiple zoning of (1) HW heating supply and return (wall hung rads), and (2) potable water supply, there are a lot of penetration points.

Asked By Oak Orchard | Feb 27 13
7 Answers

Studor vents or vent stack?

I was told by a plumber today that the local code allows for Studor Vents instead of the old tried & true plumbing vent stack. The Net Zero homes they are doing are cutting back on the holes in the roof and the plumbers are using Studor Vents.

On my custom build, should I go Studor or old school vent stack (one 2" stack through the roof)?

Any cons to the Studor?

Asked By Peter L | Mar 14 17
1 Answer

Vented and unvented roof combo

Is it possible to have a combination vented and unvented roof assembly? I own a house in southern Maine that has a vented roof. The house also has cathedral-style ceilings in two upstairs bathrooms, and it's the roof above these bathrooms where I've recently identified an ice dam. Because the bathrooms have skylights, where venting may by difficult, my thought was to constructed an unvented roof over those two rooms and leave the rest of the attic roof vented. I have no plans to convert this space to a livable area in the future so changing the who roof seems unnecessary.

Asked By Todd Bridgeo | Mar 14 17
4 Answers

Roofer put new 1/2" OSB over old 1/2" OSB

I recently had my roof replaced but have not paid the final bill. My roofer called me yesterday to advise me the entire north side of my house was going to need all new OSB installed.

Asked By hubbhunter | Mar 10 17
3 Answers

Insulation and new codes

Planning a renovation and addition of an existing house;

1. Climate Zone 4 - the new insulation code for ceilings is R49. Is the only way to achieve this in 2x12 roof framing to use closed cell spray foam or rigid on the exterior? Client doesn't want to use spray foam. Working to match existing roof lines and not remove the existing roof. In order to match existing roof lines there is part of the ceiling that will also be the roof.

Asked By S G | Mar 3 17
7 Answers

Basement finish - existing exterior R-5 - questions on interior insulation

I am finishing my basement in Minnesota. It is a walkout design. The walkout portion of the wall is a 2x6 wall with typical fiberglass bats and poly on the interior. All rim joists have 2" of foam spray.

My exterior concrete walls are covered with R-5 foam board protected with a thin layer of sand/rock pebbles.

I have been told and read so many ways to finish my interior insulation that I am dizzy. I have been told:
- No insulation, R-5 on exterior good enough.
- Put poly on concrete and get R-15 Kraft faced insulation between studs
- No poly at all, R-15 between studs

Asked By ZDude | Feb 28 17
Register for a free account and join the conversation

Get a free account and join the conversation!
Become a GBA PRO!