• Welcome to The Building Code Forum

    Your premier resource for building code knowledge.

    This forum remains free to the public thanks to the generous support of our Sawhorse Members and Corporate Sponsors. Their contributions help keep this community thriving and accessible.

    Want enhanced access to expert discussions and exclusive features? Learn more about the benefits here.

    Ready to upgrade? Log in and upgrade now.

Sloped slab floor (garage alteration)

E

Enrgxprt

REGISTERED
Joined
Dec 5, 2019
Messages
49
Location
New York
I have been seeing a bunch of existing attached garage alterations to habitable space..

Im wondering what you folks do/say or cite when it turns out the garage slab floor was poured on a slope (allowed) was simply tiled over or a laminate floor placed directly on without any attempt to level.

New codes require floor insulation, but if it was done 30 years ago and just being made legal now I have to apply the code in effect at the time of construction...
 
Enrgxprt said:
I have been seeing a bunch of existing attached garage alterations to habitable space..

Im wondering what you folks do/say or cite when it turns out the garage slab floor was poured on a slope (allowed) was simply tiled over or a laminate floor placed directly on without any attempt to level.

New codes require floor insulation, but if it was done 30 years ago and just being made legal now I have to apply the code in effect at the time of construction...
Click to expand...
Level matters not as there is no IRC spec...If it is a newly conditioned space it generally meets new code...Wicked ugly to get through the IRC and honestly I am not sure if it really works, but here you go...

N1110.2​

Any unconditioned or low energy space that is altered to become conditioned space shall be required to be brought into full compliance with this chapter.

Exceptions:

  1. 1.Where the simulated performance option in Section N1105 is used to comply with this section, the annual energy cost of the proposed design is permitted to be 110 percent of the annual energy cost otherwise allowed by Section N1105.3.
  2. 2.Where the Total UA, as determined in Section N1102.1.5, of the existing building and the addition, and any alterations that are part of the project, is less than or equal to the Total UA generated for the existing building.
  3. 3.Where complying in accordance with Section N1105 and the annual energy cost or energy use of the addition and the existing building, and any alterations that are part of the project, is less than or equal to the annual energy cost of the existing building. The addition and any alterations that are part of the project shall comply with Section N1105 in its entirety.
 
Having just done this - with a permit and inspections - and now wonder if it complies? I laid and shimmed sleepers and put 1 1/2" rigid foam between sleepers, ply and hardwood floor over.

FWIW the walls and ceiling are way over minimum insulation requirements and the stem walls are ICF to footing.
 
Encountered many times, nobody is ever pleased with the answer. When not a low energy space what I see most often is the floor raised to allow for adequate insulation, and to raise it to the floor level of the main house. I don't think there is a trade allowed for the slab insulation. Can't recall anyone actually digging up the foundation walls to install perimeter insulation.

There must also be a method to ventilate the new underfloor cavity space.
 
Yea, im well aware of what's required in today's code, its the 20-30 year old stuff thats a pita.. Anyone who tries to legalize something with a heavily pitched slab floor isn't gonna like me much. Poor workmanship is an exact fit. The definition states plumb, level and square. But those older codes.. ugh..
 
bill1952 said:
Having just done this - with a permit and inspections - and now wonder if it complies? I laid and shimmed sleepers and put 1 1/2" rigid foam between sleepers, ply and hardwood floor over.

FWIW the walls and ceiling are way over minimum insulation requirements and the stem walls are ICF to footing.
Click to expand...
So with an addition meeting a passing Res-check or prescriptive R-values everywhere including slab edge R values compliance with the code is not achieved.

What you did sounds good, my concern would be.. sleepers and foam is not continous insulation. An accurate UA calculation (if provided) might let me state that the code was substantially met.

If you had continous slab insulation as shown in res-check web AND sleepers center in the field, you should be golden.
 
Enrgxprt said:
So with an addition meeting a passing Res-check or prescriptive R-values everywhere including slab edge R values compliance with the code is not achieved.

What you did sounds good, my concern would be.. sleepers and foam is not continous insulation. An accurate UA calculation (if provided) might let me state that the code was substantially met.

If you had continous slab insulation as shown in res-check web AND sleepers center in the field, you should be golden.
Click to expand...
I did think the ICF - 2" of foam both sides of concrete stem walls to 4' below slab - would cover slab edge. (Slab floats inside stem walls.)
 
A garage conversion isn’t exactly posh. The typical effort here in California is Red Guard over a cracked slab and an inexpensive composite floor.
It’s not to say that everyone is affected, but a slanted floor can make people quite uncomfortable. It is a subliminal irritation.
 
I will say this, I'm in climate zone 4C and have never seen a single residential house or under 5 story apartment building with slab edge insulation, ever.

Even though it is required under ASHRAE 90.1 and in our energy code (OEESC) I've never seen it installed. I can see that my county has required crawlspace ventilation due to radon so I guess that negates any slab-edge insulation, but that doesn't explain how apartment buildings with either slab-on-grade or unvented crawspaces are getting away with it.
 
Penguin87 said:
I will say this, I'm in climate zone 4C and have never seen a single residential house or under 5 story apartment building with slab edge insulation, ever.

Even though it is required under ASHRAE 90.1 and in our energy code (OEESC) I've never seen it installed. I can see that my county has required crawlspace ventilation due to radon so I guess that negates any slab-edge insulation, but that doesn't explain how apartment buildings with either slab-on-grade or unvented crawspaces are getting away with it.
Click to expand...
No way? People don't build to code?
 
Do you allow either of these details? I know exposed foam can be covered but does not seem as maintenance free as these.
 

Attachments

  • 021245089-slab-on-grade_xlg.jpg
    021245089-slab-on-grade_xlg.jpg
    116.4 KB · Views: 2
  • bevel-foam.png
    bevel-foam.png
    283 KB · Views: 2
steveray said:
Really sucks at garage doors.....They make an insulated threshold.....Structural engineers seem to hate it too....
Click to expand...
Never lived in a house with an insulated garage. :) I do like the thick wall and foam fully under it without bevel but not sure that 4 or 6" "curb" meets code.

Probably prejudiced because I like thick walls with deep window sills and seats aesthetically.
 
We have a readily accepted, state-provided 'garage conversion' detail here that allows pt sleepers on the concrete floor, 6mil VB with pt joists and decking over rigid insulation. Insulating the floor is always the issue with these garage conversions and ceiling heights are usually a concern with this application.
 
bill1952 said:
Never lived in a house with an insulated garage. :) I do like the thick wall and foam fully under it without bevel but not sure that 4 or 6" "curb" meets code.

Probably prejudiced because I like thick walls with deep window sills and seats aesthetically.
Click to expand...
I was speaking commercial garages....I think 2021 brought in reduced requirements for garages that are not lived in to not meet what a house has to.......
 
bill1952 said:
Do you allow either of these details? I know exposed foam can be covered but does not seem as maintenance free as these.
Click to expand...

Yes, I am aware of them. I'm just commenting generally from doing "site walks" in my city & neighborhood of under-construction buildings and just never see slab/foundation insulation on small - to - mid residential projects. I'm guessing it has to do with our requirement for ventilated crawlspaces. Maybe they are insulating under the floor joists instead.
 
Penguin87 said:
Yes, I am aware of them. I'm just commenting generally from doing "site walks" in my city & neighborhood of under-construction buildings and just never see slab/foundation insulation on small - to - mid residential projects. I'm guessing it has to do with our requirement for ventilated crawlspaces. Maybe they are insulating under the floor joists instead.
Click to expand...
Required ventilated crawl space, slab on grade is prohibited?
 

N1113.1​

Any space that is converted to a dwelling unit or portion thereof from another use or occupancy shall comply with this chapter.

Exception: Where the simulated performance option in Section N1105 is used to comply with this section, the annual energy cost of the proposed design is permitted to be 110 percent of the annual energy cost allowed by Section N1105.2.
INSIGHTS (1)

N1113.1.1​

Any unconditioned or low-energy space that is altered to become a conditioned space shall comply with Section N1108.
 
You must log in or register to reply here.
Back
Top