Insulating a Basement

[Mini Me]

I am renovating my wife's sewing room (7.0 x 9.0 x 2.5 metres) and I want to ask a question about insulation and you guys would be far more expert than anyone I know in Oz. It is a basement situation with only one wall open to light and the floor above is my workshop which has zero insulation between the top and the lower basement and I intend to put a suspended ceiling in the basement because I can then run and access all services through the ceiling. I am also considering putting batts in attached to the under surface of the top floor.

We live in a temperate climate, lows in the 40's (F) and highs in the 110 to 120 range, the highs are not the problem only the lows. The building walls are concrete block cement filled and what I propose to do is build internal timber walls with Gyprock (drywall) and stand them up with a 200mm air space between the framed wall and the concrete block walls. The room temperature in the winter stays very low maybe in the fifties and I am wondering if I insulate the timber internal wall will it have enough effect to be worthwhile. The area is heated by heat pump reverse cycle AC but as things stand it does not do enough due to the heat going straight through the pine panelling now directly attached to the concrete walls. Any advice you might offer would be very much appreciated.

The insulating batts we get top out around R5 so nothing like you would get, would a R5 single layer do enough to be worthwhile? I think I know what the ultimate answer and that is to install under floor heating but the budget does not stretch that far and very few people in our region do it and I have found the suppliers are not interested in a job this small even if I had the budget.

 

[Tom the Remodeler]

It's ben several years since I've insulated a basement, but a big consideration to keep in mind with any building assembly is how you're handling bulk water, air, water vapor, and insulation, in that order.

So, assuming you don't have an issue with bulk water movement, you'll want to make sure you're controlling air movement and water vapor, and that your insulation method won't adversely affect those two elements.

The most common example I see in my work is folks will insulate their basement in ways that result in a condensing surface, which then results in mold or mildew development, which usually requires extensive work to remedy.

Joe Lstiburek has written a series of books about appropriate building assemblies, might be worth checking out (you can get PDF copies as well). I'm linking to the Cold Weather version, but you can search for other climate zones: Builder's Guide to Cold Climates:https://buildingscience.com/bookstore/books/builders-guide-cold-climates

 

[Mini Me]

Tom, thanks for your reply, we don't live in a very humid climate at all and the room would never be sealed to the extent I think happens in very cold climates and it is never subject to cooking, showers etc. It does have a solar driven exhaust fan that has proven to be very worthwhile in changing the air over during the day and removing the musty atmosphere caused by water leaks which is one of the fixes being done during the renovation. Basements are pretty rare here so anything about them is greatly appreciated.

 

[Packard]

I’ve been told that in my area there are building codes to adhere to.  When you go to sell your house, not adhering to the code might bite you.  Check that out.

I’ve heard that you need pressure treated framing and water resistant sheet rock for the framing.  I suspect that requirement varies with the jurisdiction.

I would do some research on the codes first.

 

[twistsol1]

As noted above, first contact your local building authority and ask what the requirements are. Where I live, there are no code requirements for insulation below grade. Where I live, temps range from -30F to 100F with almost zero humidity in the cold weather and high humidity in the summer.

What I did when I finished my basement a couple of years ago is a hybrid between what the builder installed for the unfinished basement and what I added when finishing it. This was recommended, but not required by our local building department

The builder glued 3/4 inch foil face foam insulation to the concrete block and used foil tape to seal all the seams. Added closed cell spray foam along the floor and the top of the wall. The foil facing is required as a vapor barrier for foam < 1 inch thick. The wall shown is below grade on the right and fully exposed on the left

View attachment 1

I then framed in a wall about half an inch from the foil faced insulation and insulated that with fiberglass batts.

View attachment 3

View attachment 4

The areas I insulated are fully below grade so the builder didn't add any insulation at all. I used 2 inch rigid foam glued to the concrete block and caulked and taped the seams. Everything else was the same as above.

View attachment 2

View attachment 5

 

[Tom the Remodeler]

I would avoid pressure treated lumber in a basement, unless required by your local code official. Utilizing ACQ treated lumber would require that all of your later building products would be compatible (triple hot dipped galvanized, epoxy coated, stainless, or otherwise properly treated), including your drywall screws, trim nails, etc....

I've been using borate-treated plates in lieu of pressure treated lumber for indoor applications where there is contact with a wicking cementitious surface. These plates are rot resistant (rated for concrete contact), without all of the extra headaches of working with traditional pressure treated lumber.

 

[usernumber1]

You would benefit from this guide  produced by Building Science Consulting Inc. (now merged with RDH) in partnership with Building
Science Corporation, for the Canadian Urethane Foam Contractors Association Inc.

page 8 talks about basements specifically.

They discuss open cell, closed cell and a hybrid between spray foam and insulated sheathing. they also talk about vapor requirements and issues at every part of the building.
https://www.rdh.com/resource/canadian-spray-foam-guide/

or direct link
https://www.cufca.ca/docs/CUFCA_SPF_GUIDE_2013_Final_Xerox_Press.pdf

 

[Packard]

This is all I could find online.  They mention the maximum R-value for insulating basements.  I’m not sure I understand that.

Note:  This is a Minneapolis spec.
https://www.dli.mn.gov/sites/default/files/pdf/section-R402-basement-walls.pdf

 

[Tom the Remodeler]

This is all I could find online.  They mention the maximum R-value for insulating basements.  I’m not sure I understand that.

Note:  This is a Minneapolis spec.
https://www.dli.mn.gov/sites/default/files/pdf/section-R402-basement-walls.pdf

As you note Packard, this is the local building code for Minneapolis which is Zone 6, not sure which Zone Mini Me is in.

The maximum r-value mentioned in the code is for the maximum R-value of insulation (other than closed cell foam) on the interior side of the foundation (R-11). So, they want a minimum foundation assembly R-value of R-15, with a minimum exterior R-value of R-10, with the interior insulation R-value not to exceed R-11 (unless closed cell foam).

So, if you were to go by code minimums, you'd put R-10 outside the foundation, R-5 inside the foundation.

Or, you could put R-15+ on the outside of the foundation and not need any interior basement insulation.

Either way, unless you're using closed cell foam you're not allowed to exceed an insulation assembly on the interior of the foundation which exceeds R-11.

 

[Tom the Remodeler]

As a quickie follow-up, I'm assuming that they're limiting the permissible interior R-value to 11 in an attempt to keep the interior face of the foundation "warm", or above the dew point so it does not become a condensing surface. I've ripped out several finished (and insulated!) basements that were just awful, nasty, moldy messes, mostly due to poor moisture control, lack of mechanical ventilation, and poor planning regarding controlling condensing surfaces.

This is very similar to the current thinking on above-grade wall insulation where the building science is telling us that a certain percentage of the insulation (as dictated by tables) should be on the "weather" side of the wall sheathing (usually outside the air/water/vapor control layer(s)), the idea being to keep the interior of the structural wall sheathing "warm" and above the dew point so it's not a condensing surface.....

 

[woodbutcherbower]

Do you have 8' x 4' foil-lined Celotex, Kingspan or Quinntherm polyurethane foam blocks over there in various thicknesses? And 1200-gauge polythene DPM sheet on a roll? And Blackjack liquid floor DPM or equivalent? And electric underfloor grid heating mats-on-a-roll which run off a 13-amp supply?

 

[Mini Me]

Do you have 8' x 4' foil-lined Celotex, Kingspan or Quinntherm polyurethane foam blocks over there in various thicknesses? And 1200-gauge polythene DPM sheet on a roll? And Blackjack liquid floor DPM or equivalent? And electric underfloor grid heating mats-on-a-roll which run off a 13-amp supply?

Thanks WB, I will have a look around but in general no one really does any sort of insulation well in Oz just lip service at best. One thing that is a bit different where I live is that the local council who control building standards have a policy of allowing anything internal as long as the externals of the building are as approved by them. My neighbour recently gutted his home back to the frame and rebuilt the interior and the council was not interested in it at all.

 

[Cheese]

FWIW...I've used 1" Celotex for attic chutes and it provides a higher R Value because of the foil liner. It's good stuff, but it's been difficult to find lately.

 

[woodbutcherbower]

[member=58818]Mini Me[/member] Ah OK. Standard method over here for above-ground applications is as per pictures below. This was a small garage which the customer wanted to use as a home office. Below-ground applications are identical, but the rear of the studwork gets lined with 1200-gauge polythene to act as a damp membrane;

1 Construct a stud frame using 3” x 2” CLS timber at 600mm centres. Add horizontal 600mm noggins to maintain spacing;

[attachimg=1]

2 Cut Kingspan/Celotex/Quinntherm/Recticel to size and insert into framework. This particular one is 3” thick and is the full depth of the stud frame. It needs to be accurately cut so it’s a tight push-fit with no air gaps;

[attachimg=2]

3 Board over with plasterboard. In the case of ceilings (since that’s where most of the heat loss occurs) I use insulated board which has an additional inch of polyurethane foam bonded to one side;

[attachimg=3]

Skim plaster and you’re done;

[attachimg=4]

The floor is treated using 2/3 coats of Blackjack. This is basically quick-drying bitumen in a can. The floor is then flattened (millpond) using self-levelling compound.

Kevin

Edited to add - it’s like a sauna in there during the winter. The only heating is a small 2kW fan heater which the customer runs for 30 minutes once in awhile. In the summer, he uses a small portable AC unit which vents to the outside through a small pipe.

 

[bobtskutter]

[member=75780]woodbutcherbower[/member] thank you kindly for sharing the details of insulating that old garage, I have something very similar planned for my garage (once I get it extended).

I also plan to add a simple HVAC system with air scrubber, dehumidifier and heater.

Please can I double check, you said paint the floor with blackjack and then use self leveller?

Thanks, Bob

 

[woodbutcherbower]

[member=76043]bobtskutter[/member] Yes mate. You need ‘Blackjack Liquid DPM’ - available at most builders merchants. 2 or 3 coats with half a day in between for it to thoroughly set. I think Toolstation also stock it.

Once fully dry - SLC straight over the top. Best product to use is a fibre-reinforced one which won’t move or crack when the concrete expands and contracts with temperature over the year. My favourite is Mapei 3240 - Screwfix stock it. A 10-15mm layer is fine.

Good luck with the project !!

Kevin

Edit = I just checked through the WhatsApp thread and here’s the finished result once the customer had painted and carpeted it  [smile]

[attachimg=1]

 

[bobtskutter]

Thank you, much appreciated!
Regards
bob

 

[Mini Me]

Thanks for the pics, I am going to stand the frame 200mm off the block wall because there are engaged piers which protrude into the room and that way I get a straight wall and cover the piers. The piers support 7 metre beams across the room which support the top floor. I built this when I was young and stupid and did not know better and it took a year to dig the hole because we in those days the small machines did not exist and it was all pick and shovel.

 

[Michael Kellough]

Kevin said “I use insulated board which has an additional inch of polyurethane foam bonded to one side”

Looks like another great material that I don’t think we have in the States.

 

[woodbutcherbower]

I think it's largely down to construction methods over here, [member=297]Michael Kellough[/member]. Most UK buildings are double-skinned brick or aerated concrete block, unlike NA where timber framing is used much more extensively - plus we have many hundreds of thousands of buildings which are more than 200 years old, with roofs built using two-centuries-old materials and technology. The insulated plasterboard (mostly used for ceilings) comes in a variety of thicknesses up to a 4" layer of insulation bonded to the board. When this material's used in conjunction with a stud frame and a decent thickness of PU insulation as per the photos, the heat loss is effectively zero.

We also have other useful material such as plasterboard skinned on one side with aluminium foil to act as a vapour trap. All of  this material needs to be plastered after installation. Drywall (pre-plastered board which needs to be taped, filled and sanded) only usually gets used in large commercial applications over here.