Basement build | Insulation installation

I would do the regular Batt Insulation. As for no insulation behind the studs if you have some space between the wall and studs you can stuff some insulation just behind the studs. You could also spray some sprayfoam right behind it. Another more expensive option would be do Spray & Batt 2" of spray foam on the full concrete wall & then regular batt between the studs.

bigfootcanada wrote: ↑ Hi All,

I am building my basement as per the permit and the current insulation installed by the builder is old. I believe R8 value or so as the house is 2005 built. I need to upgrade it to R20.
Currently, the insulation is a blanket installed on the top half wall. I am thinking to take down the old insulation and put the new for all 8 ft of wall.

My question is, which way is better - to put the new insulation (blanket insulation) attached to the wall as the builder did or put the batt insulation between the studs after framing?

My concern is - one insulation contractor said that when you put batt insulation between studs the area acquired by studs is not insulated (like there is no insulation behind the studs) and that will remain cold. He suggested putting blanket insulation as the builder does.

I have seen many people suggesting and doing batt insulation between studs as this also gives some space for moisture drying up.

What are your thoughts or recommendations?

This is what i did with my place when i built a legal basement suite.

i tore down the "finished basement" that was there already and saw that they had just left the original builder insulation. I tore it all out, but left the studs as they were not up against the concrete and then i did a spray foam insulation. I put down 1.5" rigid foam on the floor covered by plywood and the basement is now as comfortable as anywhere in the house.


for your purposes i would tear out the builder, put rigid foam up against the concrete, tape and seal, then put up your framing and you can then put up batt insulation as it's only R15 unless you go with 2x6.
also don't forget the flooring, you may think it's not necessary as you are not living there, but tenants may find other creative ways to stay warm if the floor is ice cold..e .g. space heaters
not to mention if you use any of the basement yourself it's nice if it's warm, so putting down rigid foam and covering it with plywood and securing it with tapcons are a good way to do it.

I would put 2" XPS R10 foam insulation directly on the concrete, then put 2x4 framing in front of the XPS, and then R14 Roxul insulation placed in between the 2x4 studs. This will give you R24.

Using 2" XPS R10 counts as a vapour barrier, so you won't need another vapour barrier before the drywall, while 1.5" XPS R8 won't count as a vapour barrier, and will require a vapour barrier before the drywall. You don't want to create a two vapour barrier mould sandwich, and should avoid having the vapour barrier on the warm side of the studs as you will likely get mould growth in the stud cavity, hence, using the 2" XPS.

We did Roxul Comfortboard against the foundation wall, studded in front of it and put Roxul Comfortbat between the studs. Our basement is probably the warmest room in the house!

The_Madz wrote: ↑This is what i did with my place when i built a legal basement suite.

i tore down the "finished basement" that was there already and saw that they had just left the original builder insulation. I tore it all out, but left the studs as they were not up against the concrete and then i did a spray foam insulation. I put down 1.5" rigid foam on the floor covered by plywood and the basement is now as comfortable as anywhere in the house.


for your purposes i would tear out the builder, put rigid foam up against the concrete, tape and seal, then put up your framing and you can then put up batt insulation as it's only R15 unless you go with 2x6.
also don't forget the flooring, you may think it's not necessary as you are not living there, but tenants may find other creative ways to stay warm if the floor is ice cold..e .g. space heaters
not to mention if you use any of the basement yourself it's nice if it's warm, so putting down rigid foam and covering it with plywood and securing it with tapcons are a good way to do it.

cba123 wrote: ↑I would put 2" XPS R10 foam insulation directly on the concrete, then put 2x4 framing in front of the XPS, and then R14 Roxul insulation placed in between the 2x4 studs. This will give you R24.

Using 2" XPS R10 counts as a vapour barrier, so you won't need another vapour barrier before the drywall, while 1.5" XPS R8 won't count as a vapour barrier, and will require a vapour barrier before the drywall. You don't want to create a two vapour barrier mould sandwich, and should avoid having the vapour barrier on the warm side of the studs as you will likely get mould growth in the stud cavity, hence, using the 2" XPS.

mrweather wrote: ↑ We did Roxul Comfortboard against the foundation wall, studded in front of it and put Roxul Comfortbat between the studs. Our basement is probably the warmest room in the house!

OP, what these three posters said. This is the latest and most up to date way for finishing basement. Foam insulation that counts as vapour barrier right up against the wall.

Also, if you find a YouTube video on renovision , he basically puts a couple of globs of the adhesive and presses it against the wall. Not too hard or all the way, so that there is a very narrow air gap behind the foam board in case of any condensation formation or water seepage, it will just flow down to the ground and to the drain hole, assuming you have proper subfloor setup to allow for that continuity.

Don't forget to insulate the rimjoists!

cba123 wrote: ↑ I would put 2" XPS R10 foam insulation directly on the concrete, then put 2x4 framing in front of the XPS, and then R14 Roxul insulation placed in between the 2x4 studs. This will give you R24.

Using 2" XPS R10 counts as a vapour barrier, so you won't need another vapour barrier before the drywall, while 1.5" XPS R8 won't count as a vapour barrier, and will require a vapour barrier before the drywall. You don't want to create a two vapour barrier mould sandwich, and should avoid having the vapour barrier on the warm side of the studs as you will likely get mould growth in the stud cavity, hence, using the 2" XPS.

This is the very best DIY way to do it and save space. At the cottage where we heat with propane, we laid roxul batts down behind the studs, studded, then batted in between studs. For rim joist, we got a DIY spray foam kit to seal it up.

The best pro way is of course spray foam. Likely about 2.5 times the best DIY way. My buddy is in progress of having to re-do his basement due to water infiltration (he dug a ditch and added sump holes and the whole 9) and he was able to have professionally done spray foam for $5700 vs styrofoam and batt DIY install for $2k or so. One of his deciding factors (after a very long basement reno) was that he didn’t have to do it. He had moved 8000 pounds of concrete by ladder out of his basement in the previous month.

I did the 2" XPS glued a long the exterior walls and then did R14 Roxul between the studs when I did my basement back in 2016. IIRC that totals up to R24?

Funny thing is the building inspector wanted the poly up before the drywall. So I did it, ripped it down when he left and drywalled.

Make sure you tuck tape all the seams of the XPS and use some canned spray foam where it meets the rim joists and the floor. I also cut and installed 2" XPS in to the header where the rim joists are using glue and spray foam.

Side note: make sure you have adequate air flow in your basement to your HVAC. Well placed and sized returns and vents.
Try to create a crossflow. Try to bring your return down and vents up or vice versa.

tebore wrote: ↑
Side note: make sure you have adequate air flow in your basement to your HVAC. Well placed and sized returns and vents.
Try to create a crossflow. Try to bring your return down and vents up or vice versa.

Just my opinion, but the average person really shouldn't mess with the HVAC system. Of course funds matter more than anything, but if the HVAC system is going to be touched, I would pay for a professional to assess the entire system and try to keep it as balanced as possible. It's far more complicated than most realize.

If you add a return or change something else, it can throw off the entire system, sometimes even cutting off all airflow to one or more rooms.

Most homes don't have a properly balanced HVAC system

The air space required by code(permit) is 1" between the studs and the wall. If we put 2" XPS foam on the wall, that will increase the space between studs and the wall, and decrease the area/room space. Unfortunately, I don't have that flexibility.

Shaner wrote: ↑ Just my opinion, but the average person really shouldn't mess with the HVAC system. Of course funds matter more than anything, but if the HVAC system is going to be touched, I would pay for a professional to assess the entire system and try to keep it as balanced as possible. It's far more complicated than most realize.

If you add a return or change something else, it can throw off the entire system, sometimes even cutting off all airflow to one or more rooms.

Most homes don't have a properly balanced HVAC system

Most unfinished basements have vents in an unbalanced manner for the basement anyway.
Most people when they finish a basement overlook this aspect.

Ideally you'd have a mechanical engineer review your current HVAC plan and revise it to the new layout.

bigfootcanada wrote: ↑ The air space required by code(permit) is 1" between the studs and the wall. If we put 2" XPS foam on the wall, that will increase the space between studs and the wall, and decrease the area/room space. Unfortunately, I don't have that flexibility.

Why are you concerned with the loss of 2" on an exterior wall? In the grand scheme of things, taking for example a 10X10 foot room, that 2" is minuscule and I really doubt you would notice.

bigfootcanada wrote: ↑ The air space required by code(permit) is 1" between the studs and the wall. If we put 2" XPS foam on the wall, that will increase the space between studs and the wall, and decrease the area/room space. Unfortunately, I don't have that flexibility.

If losing 2" of width and length will cause that much heartache, maybe reconsider the layout?

rcmpvet wrote: ↑ Why are you concerned with the loss of 2" on an exterior wall? In the grand scheme of things, taking for example a 10X10 foot room, that 2" is minuscule and I really doubt you would notice.

you are right, it's not about losing space or I am noticing anything. It's about building inspectors. For example, in Brampton, if there is a basement apartment, it has to have at least 1 bedroom with a minimum of 100 sqft.
Now they already mentioned at least and minimum - if you reduced even an inch from there, then don't know what the inspector is gonna say. They measure.

cba123 wrote: ↑ I would put 2" XPS R10 foam insulation directly on the concrete, then put 2x4 framing in front of the XPS, and then R14 Roxul insulation placed in between the 2x4 studs. This will give you R24.

Using 2" XPS R10 counts as a vapour barrier, so you won't need another vapour barrier before the drywall, while 1.5" XPS R8 won't count as a vapour barrier, and will require a vapour barrier before the drywall. You don't want to create a two vapour barrier mould sandwich, and should avoid having the vapour barrier on the warm side of the studs as you will likely get mould growth in the stud cavity, hence, using the 2" XPS.

This is exactly what I plan to do for my basement but maybe use GPS instead

bigfootcanada wrote: ↑ you are right, it's not about losing space or I am noticing anything. It's about building inspectors. For example, in Brampton, if there is a basement apartment, it has to have at least 1 bedroom with a minimum of 100 sqft.
Now they already mentioned at least and minimum - if you reduced even an inch from there, then don't know what the inspector is gonna say. They measure.

But you're ok doing 1" board? I really can't imagine any inspector on earth failing your renovations due to that 1". Not when you're talking about 1" out of 100 sqft

bigfootcanada wrote: ↑ The air space required by code(permit) is 1" between the studs and the wall. If we put 2" XPS foam on the wall, that will increase the space between studs and the wall, and decrease the area/room space. Unfortunately, I don't have that flexibility.

Not sure what you are talking about here. There is no 1" air gap requirement in the building code. Maybe you are talking about the 1" air gap needed between the inside side of exterior bricks and the exterior side of the sheathing of above grade walls?

The distance from the interior side of the basement foundation to the exterior side of drywall would be 2" XPS + 3.5" 2x4 stud + 0.5" drywall equals 6".

If you wanted to use only batt insulation, then you would need a 2x6 stud wall to get to R20, which will need the same 6" of distance from the interior side of the basement foundation, but will have the downside of thermal bridging through the studs.

The following is an excerpt from section 6.2.4 from the nrcan website...where it says to build the stud wall in direct contact with the XPS insulation.
https://www.nrcan.gc.ca/energy-efficien ... 15639#a6-2

6.2.4 Frame wall with batt insulation and rigid board insulation
This method involves gluing rigid board insulation to the foundation wall and then covering it with a frame wall incorporating batt insulation. The result is higher insulation values with less loss of interior space, a very good reduction of thermal bridging and no need for an additional moisture barrier. It works best if the basement wall is even and vertical (i.e. poured concrete or concrete block) as the board is fairly rigid. Use only moisture-resistant board insulation such as extruded polystyrene or Type IV expanded polystyrene.

Preparation
Follow the preparations required in Part 6.2.1, How to insulate inside the basement using only rigid board insulation.

Installation
Using rigid board insulation with at least RSI 1.76 (R-10), secure and seal it to the foundation by applying foam-compatible adhesive around the perimeter of the foam board before fastening it to the wall. If any mould were to develop behind the insulation it would be contained. Air sealing the foam board to the wall creates an air and moisture barrier somewhat equivalent to spray foam. Special mechanical fasteners can be used if you have any sensitivity to the glue. Install the insulation snugly to eliminate air circulation at the edges. Use urethane foam sealant and technical tape to seal all joints and interParts of the foam board.

Next, install the wood-frame wall directly in contact with the rigid board insulation. Follow the techniques detailed in Part 6.2.3, Frame wall with single or double layer of batt insulation.

Adding additional insulation
The frame wall can now be roughed in for any wiring and plumbing and insulated as noted previously in Part 6.2.3, Frame wall with single or double layer of batt insulation. For details on treating the joist area, see Part 6.2.6, Joist header space.

Finishing
Do not use a polyethylene air and vapour barrier with this approach, as there is a risk of creating a double vapour barrier with the foam board. Instead, use either the smart barrier or the ADA method.

If you are using smart barrier, leave enough of the film at the top to connect to the air barrier in the joist space.

If you are using the ADA method, pay strict attention to proper air and vapour sealing, including a layer of vapour barrier paint. Any exposed foam insulation may require fire protection as per code requirements.

Adding my 2 cents as OP is getting mixed information. From the OBC SB-12, Basement walls require R20ci (ci means continuous insulation), this can be substituted with R12+R10ci. The air space that has been mentioned is not covered in the OBC, but the only way to obtain "continuous insulation" is to have a gap. My typical standard basement wall assembly is 5" from the foundation wall; 1" gap, 2x4 studs, 1/2" GWB; 2lbs closed cell spray foam insulation. I wouldn't suggest rigid as it will take up a lot of time for installation, then add batt and V.B. The closed cell acts as a VB, and the quick spray will fill in the gap, and all nooks and crannies. Your basement would be a much tighter seal than with rigid.

OP if you're afraid that the inspector will bust out his tape, then go with a 1-1/2" gap. However, I've never seen an inspector measure the gap to be honest, they have other things to inspect.

Faemow wrote: ↑ Adding my 2 cents as OP is getting mixed information. From the OBC SB-12, Basement walls require R20ci (ci means continuous insulation), this can be substituted with R12+R10ci. The air space that has been mentioned is not covered in the OBC, but the only way to obtain "continuous insulation" is to have a gap. My typical standard basement wall assembly is 5" from the foundation wall; 1" gap, 2x4 studs, 1/2" GWB; 2lbs closed cell spray foam insulation. I wouldn't suggest rigid as it will take up a lot of time for installation, then add batt and V.B. The closed cell acts as a VB, and the quick spray will fill in the gap, and all nooks and crannies. Your basement would be a much tighter seal than with rigid.

OP if you're afraid that the inspector will bust out his tape, then go with a 1-1/2" gap. However, I've never seen an inspector measure the gap to be honest, they have other things to inspect.

This is correct. R10 rigid insulation with a 2x4 stud (R12/R14) is acceptable as per OBC. There is no air gap requirement between the studs and the foundation.

I don't think you need to be worried about the building inspection. You need to submit a drawing for the initial permit, and if the city approves your drawing and you follow it then all is well. You wouldn't need to worry about a tear down.