I've got a 12x16 elevated sunroom with a very thin berber carpet directly on what appears to be planks of tongue and groove wood flooring. The bottom of these planks can be seen from below the sunroom outside, and are supported by 2x8 joists that run the 12', (roughly 16" O.C.)

We've placed a thick wool rug on top, but it's only 9x12ish, and the room is only nice in Spring and Fall. Space heater helps in the winter and window AC in the summer but both seem incredible wasteful given the absence of insulation. I suppose the walls have something, but with 10 windows (double pane, but older) on 3 walls it's just not great.

How best to insulate the floor? There is a slight step down from the house into the sunroom, so I could imagine maybe 1" of insulation that might sit directly on top of the wood, but it would have to be fully weight bearing such that we could place furniture and walk on it without any permanent compression.

Of course I can also do something on the underside as well, I am thinking cut sections of rigid foam for that, but I will have an opportunity to work on the inside soon and want a game plan.



Edited 1 time(s). Last edit at 05/25/2022 03:33PM by mikebw.

Underneath would be best.

Wall to wall carpet w/ padding is simplest.

Maybe a combo?

I enclosed a concrete-floored porch that sits atop a garage. The garage has a low ceiling so I did not want add thickness there. And I was limited on the topside, as well, to match the level of the main house. To insulate the floor, I tacked down 2x3 sleepers flat in joist spacing, and filled the voids with rigid foam. I put OSB on top of that. That combination brought the floor up to near perfectly match the main house. Then padded carpeting on one part and luxury vinyl tile on the other. I don't notice a cold floor on the vinyl or the carpet in that room.



Edited 2 time(s). Last edit at 05/25/2022 03:46PM by Acer.

Do the walls and ceiling have insulation? If the roof/ceiling isn't insulated, insulating the floor probably isn't going to help much.

For the floor, I'd access the bays between the joists from underneath, fill them with rigid foam or fiberglass, and then attach sheathing to the bottom of the joists.

Rigid foam with an underlayment on top of it can be weight bearing, and will insulate the whole floor more evenly. Would have to check what is currently available.

Insulating underneath just between the floor joists will also work. But the joists themselves may have lower insulating value than the rigid foam.

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JoeH
Rigid foam with an underlayment on top of it can be weight bearing, and will insulate the whole floor more evenly. Would have to check what is currently available.

Insulating underneath just between the floor joists will also work. But the joists themselves may have lower insulating value than the rigid foam.

Sleepers would have about the same insulating value as the joists.

If the T&G flooring is visible from below, a vaport barrier under an overlayment, with batts underneath between the joists and sheetrock could have a big effect, regardless of the windows. There could be a lot of air getting past the T&G.

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Edited 1 time(s). Last edit at 05/25/2022 05:52PM by lost in space.

A lot of good ideas here.

I'd consider unfaced fiberglass batts with rigid foam under, sealed with spray foam around the edges. Another option, depending on budget, would be to have spray foam installed (or get a kit and install yourself.

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lost in space

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JoeH
Rigid foam with an underlayment on top of it can be weight bearing, and will insulate the whole floor more evenly. Would have to check what is currently available.

Insulating underneath just between the floor joists will also work. But the joists themselves may have lower insulating value than the rigid foam.

Sleepers would have about the same insulating value as the joists.

If the T&G flooring is visible from below, a vaport barrier under an overlayment, with batts underneath between the joists and sheetrock could have a big effect, regardless of the windows. There could be a lot of air getting past the T&G.

You wouldn't need the sleepers. The rigid foam goes down in a single layer over the existing tongue and groove decking. I recall coming across products that had the finish or underlayment attached directly to the rigid foam panels as well.

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John B.
Do the walls and ceiling have insulation? If the roof/ceiling isn't insulated, insulating the floor probably isn't going to help much.

For the floor, I'd access the bays between the joists from underneath, fill them with rigid foam or fiberglass, and then attach sheathing to the bottom of the joists.

As I said the walls probably have some insulation, but the windows take up roughly 33% of the total wall area so that doesn't help. It has a fully shingled roof with gable vent. I assume there is insulation.

There is a seating area below the sunroom outside, so I would want to make it look nice. Sheathing could be painted to match the surroundings, although I would need to work on relocating or making separate access to some outlets and wires that currently run along the joists.

It looks like XPS panels can be had as thin as 1" with R=5. Compressive Strength (minimum) ranges from 20 up to 100 psi. Fasten that to the decking and then a roll of carpet on top?

Would would be a reasonable minimum psi rating for foot traffic and furniture? A 4-legged chair with a 200 pound person could easily generate 50psi on each foot as a static load, forget about when they actually plop down into it. Not sure what the cost ranges from for the 50-100psi rated panels.

I could probably do a layer of masonite on top of the XPS adding another 1/8". That's really hard stuff. Then carpet but no pad? Sure would be nice if the XPS came in 1/2 or 3/4.

What about cork? (he says to himself).

EDIT:

It looks like Cork has R value of 3.6-4.2 per inch¹, and much better compressive strength starting at 1mPA which is ~145 psi². Of course it is more expensive than the XPS at about $5/sqft.³ versus about $1 for 1", but it would not require any other covering for looks or protection. Probably would still lay an area rug though.


1- [thermalcorksolutions.com]

2- [en.wikipedia.org]).

3- [www.amcork.com]



Edited 1 time(s). Last edit at 05/26/2022 09:18AM by mikebw.

If you want cork in panels look at [www.widgetco.com]
I bought their panels 2’x3’, I think, to use as a floor in my laundry room
I just used wood glue to stick them down then sealed the top with a light gray stain
It worked great, and it’s very quiet
The panels were a lot cheaper than regular cork floor tiles and were quicker to install, since they were larger.
They are listed as underpayment, but I used them as the finished floor. Cork is cork. Seal it and you are good to go
In the panels the cost is as low as 48¢sf for the 1/8”, but you might want to go with 1/4” for more insulation value but still only about $1sf
They also have 1/2” and you could use more than one layer if you wanted thicker.

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Roswell, GA (Atlanta suburb)



Edited 3 time(s). Last edit at 05/26/2022 12:58PM by rgG.

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rgG
If you want cork in panels look at [www.widgetco.com]
I bought their panels 2’x3’, I think, to use as a floor in my laundry room
I just used wood glue to stick them down then sealed the top with a light gray stain
It worked great, and it’s very quiet
The panels were a lot cheaper than regular cork floor tiles and were quicker to install, since they were larger.
They are listed as underpayment, but I used them as the finished floor. Cork is cork. Seal it and you are good to go
In the panels the cost is as low as 48¢sf for the 1/8”, but you might want to go with 1/4” for more insulation value but still only about $1sf
They also have 1/2” and you could use more than one layer if you wanted thicker.

Thanks for that.

I was just getting a quote from another cork supplier who said their 12mm panels are good for insulation but quote "NOT dense enough to be used as a flooring". They suggested I could add additional height by putting on a ~5mm glue down tile on top making it close to my 1" max (24mm) and that would be a better wearing surface.

To cover this 192 sq. ft. room it would be close to $2K for everything they recommended, with glue and the $150 polyurethane sealant.

It seems I could 4 boxes of your 1/2" for $380, and add a layer of 1/4" (2 boxes) for $190 more; so 3/4" of cork, R-2.45, $570 with free shipping- way under the other estimate!

What would you recommend I use to seal it? This area will be seeing light daily foot traffic and 2 cats in/out all day.

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mikebw
What would you recommend I use to seal it? This area will be seeing light daily foot traffic and 2 cats in/out all day.

[www.lowes.com]

Any brand of floor quality water based poly should do the job
The water based dries more quickly, doesn’t yellow, and has less odor than an oil based sealant.
Three coats is ideal for a flooring application.

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Roswell, GA (Atlanta suburb)

I think we are going to go with just the 1/2 cork as an underlayment and then do a wall to wall carpet on top. Still need to seal?

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mikebw
I think we are going to go with just the 1/2 cork as an underlayment and then do a wall to wall carpet on top. Still need to seal?

Not really. You really only need to seal if you are using as a finished surface.

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Roswell, GA (Atlanta suburb)