3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte, NC

rollandelliott

I have a rental place in Charlote, NC where the garage was converted to a living area. It has a concrete slab and an uninsulated brick footer about 8" tall around 75% of the perimeter. Above the bricks is a standard 2x4 framed wall wtih fiberglass batts.

in the colder months, Dec,jan,feb, people complain about the floor being cold. I'm sure the uninsulated brick footer is the main issue as it acts as a thermal bridge from inside to out.

What is best way to sovle this? I have a lot of 3" rigid insulation I got for cheap. Should I insulate the entire floor/slab? throw some tile board over it and tile the whole floor?

should I just dig down two feet on the outside and put rigid foam against the outside footer?

or maybe I should put the rigid foam insulation on the inside and sheet rock over it?

jonr

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

I would put foam on the floor and over at least the lower part of the walls.

vtmaps

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

rollandelliott wrote: »

should I just dig down two feet on the outside and put rigid foam against the outside footer?

or maybe I should put the rigid foam insulation on the inside and sheet rock over it?

Up here in Vermont, we would insulate the outside down to the footers (at least 4 ft down because of deep frost). You need to find some way to cover the foam where it is above grade... the foam will deteriorate if exposed to sunlight. Another benefit of insulating the outside is the thermal mass of the bricks is inside the living quarters.

It is probably much easier to insulate the inside, especially since this is a retro fit.

--vtMaps

peakbagger

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

I am not sure about North Carolina ants and termites but new England carpenter ants love to nest in foam. There are some firms that make foam treated with insecticide but its definitely something t consider. Lot to be said for insulating on the interior

jonr

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

If you put it on the outside, down 2 feet, then the edges of the slab will have a ~4 feet soil/concrete thermal path to the cold outside air. That's about R4. Put foam on the inside and it will be more like R12 to anywhere. Not as significant as it sounds, but something to consider.

If you want the most comfortable floor possible, consider adding some PEX tubing for radiant heat.

niel

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

if you are talking of them just walking on a concrete floor then i can see why they feel cold. one could put in wood flooring, but that may only reduce the effect some. most put rugs down with a good padding.

waynefromnscanada

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

I put 2 inches (wish I had 3) rigid foam on my basement concrete floor about 20 years ago, then plywood over that to spread the weight of anything that would be on the floor, and the results were/are amazing! Would I do it again? You want to believe I would!

niel

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

wayne,
north carolina doesn't get as cold as you or i would, but i'm sure there are days that they would like the insulation and plywood down too.

Ralph Day

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

Wayne, any problem with mildew or moulds? Ever smell them in the basement? I have one 8 x 10 foot section of concrete floor covered by OSB/plastic flooring. Every few years I lift the 2" foam athletic mats off and have to bleach/wipe the 2 surfaces and the concrete surface too. De humidifying uses too much power in the summer, but wood heat dries everything out nicely for the other3/4 of the year.

Ralph

waynefromnscanada

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

Ralph Day wrote: »

Wayne, any problem with mildew or moulds? Ever smell them in the basement? wood heat dries everything out nicely for the other3/4 of the year.

Ralph

Hi Ralph, no, I've had no mold or smell. I also have wood heat there in the winter and perhaps that keeps it dry. Interesting observation - - - before I insulated the floor, if I let nice warm summer air flow through the basement, moisture would build up on the cold concrete floor and it would actually get wet. Now the insulation prevents that. OH, and I forgot to mention, there is a plastic vapor barrier between the plywood and the foam insulation. The insulation is in direct contact with the concrete and any time I've checked, it's dry between the two.
On the downside, the basement is 6 feet down in ledge rock, so although it's very stable, I am struggling with a radon problem. Sealing openings etc and increasing air exchange has helped, but still too much. When initially discovered, was over the 800 mark, got it down to roughly 200, the recommended max, but I understand Health Canada is about to lower the limit to 100. Going to try drilling through the floor and exhausting any gas, but there's a fly in the ointment - - there are springs under the floor, so I may have to drill several holes to find a good air space.

animatt

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

Been following thread for a few days. Surprised to see the question of which type of insulation you have? Polyiso or polystyrene? Or other Not sure what color is it. They are used for different things. Polystrene can handle moisture better.

If currently exposed concrete floor insulating floor will make a world of difference. Also look for air leaks that could cause really cold floors. Air leak could be from windows, doors, above the sheet rock on ceiling etc. I had someone working in an attic move some insulation to run some wires. Although unseen, the floor in that area was very cold.

solar_dave

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

waynefromnscanada wrote: »

Hi Ralph, no, I've had no mold or smell. I also have wood heat there in the winter and perhaps that keeps it dry. Interesting observation - - - before I insulated the floor, if I let nice warm summer air flow through the basement, moisture would build up on the cold concrete floor and it would actually get wet. Now the insulation prevents that. OH, and I forgot to mention, there is a plastic vapor barrier between the plywood and the foam insulation. The insulation is in direct contact with the concrete and any time I've checked, it's dry between the two.
On the downside, the basement is 6 feet down in ledge rock, so although it's very stable, I am struggling with a radon problem. Sealing openings etc and increasing air exchange has helped, but still too much. When initially discovered, was over the 800 mark, got it down to roughly 200, the recommended max, but I understand Health Canada is about to lower the limit to 100. Going to try drilling through the floor and exhausting any gas, but there's a fly in the ointment - - there are springs under the floor, so I may have to drill several holes to find a good air space.

Perhaps a 2X4 frame and closed cell spray foam would be better for your radon problem.

waynefromnscanada

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

solar_dave wrote: »

Perhaps a 2X4 frame and closed cell spray foam would be better for your radon problem.

Good thought. Something to consider for sure. Thanks for the idea.

Ralph Day

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

How does a homeowner check the radon level in their basement|? Are there home kits you expose, then send for analysis? Something from way back in the 70's memory is tickleing my synapses.

Ralph

BB.

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

Here is the US EPA.gov website about radon:

http://www.epa.gov/radon/pubs/hmbyguid.html

Simple google search:

https://www.google.com/search?q=home+radon+testing

-Bill

waynefromnscanada

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

Canada and the US use different ways and therefore different numbers for measuring radon.
"The concentration of radon in the air is measured in units of becquerels per cubic meter (Bq/m³) or picocuries per litre (pCi/L). Both these units are measurements of radioactive concentration. The international community uses the becquerel per cubic meter of air (Bq/³), while the USA uses the picocurie per litre to measure radon. One pCi/L is equivalent to 37 Bq/m³."
My original 800 would be roughly 22 in the American measuring system.

mike95490

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

To seal the gas out, can you use a mortar or plaster, and put a skim coat over the walls and floor ? it would still let it "breathe" and vent moisture, but slow down the raw gas. The "modern" way is drill holes and power vent them outside, but that costs energy.

niel

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

mike95490 wrote: »

To seal the gas out, can you use a mortar or plaster, and put a skim coat over the walls and floor ? it would still let it "breathe" and vent moisture, but slow down the raw gas. The "modern" way is drill holes and power vent them outside, but that costs energy.

it won't be that bad if the vents are laid under the concrete flooring and are sealed from leaking to the air above the floor. multiple pipes would be needed in different basement areas to allow the gas to escape. pipes can also be insulated if there would be condensation.

waynefromnscanada

Re: 3" of rigid insulation on top of converted garage slab beneficial or not? Charlotte,

I wish radon smelled like skunk discharge, it wouldn't be so easy to ignore or put off doing anything about until another day.
So easy to live with a threat you can't hear, feel, see, taste or smell.