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How to draught seal yellowtongue floor boards?

I have just had to restump my 1930s house, and the old T&G has been replaced with yellowtongue. Due to the "cut-in-floor" construction method, the floor boards but up against the bottom plates of the perimeter wall, but as-per requiremetns leave a 10mm expansion gap. Through that gap ic an see straight down to the subfloor area and soil. Once i put skirting back up, that will be the only thing between the outside air and the inside of my house.

What is the best product / technique to use to seal this space?

best regards

EDIT: after looking at the installation manual for the product, it reccommends installing timber trimmers in between joists to carry the edge of the floorboards (which would also help stop draughts) is this recommendation backed up by a reconginsed standard, or is this just a manufacturer recommendation?

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Comments

JacobZ

Hi @jacobm,

Thank you for your question and welcome to the Bunnings Workshop community, it is fantastic to have you with us.

I can't say I'm certain whether this is a recognised standard or not, but it is certainly good practice to ensure the sheets are supported on all edges.

My experiences with installing yellow tongue have always involved blocking being installed wherever the boards join and at their termination against the walls. This is primarily so the board is supported on all edges, but it would also effectively block this gap, while still allowing the small expansion gap required.

It looks like you have fairly good access to the underside of your house, so my suggestion would be to install some 70x35 H3 Pine as blocking between the joists where the yellow tongue terminates at the walls. If you wanted to make it really airtight, you could put some Moroday 75 x 10mm Adhesive Foam on the top of the blocking and compress it against the yellow tongue and bottom plate of the wall before nailing it in place.

Allow me to tag some of our handy members to see if they have any other ideas, @Noyade, @DIYGnome, @Nailbag, @Dave-1.

Let me know if you have any further questions.

Jacob

Nailbag

Hi @jacobm

I definitely wouldn't be going to the extend of using timber. There is nothing structural here and timber wont provide an air seal without sealant.

The adhesive foam @JacobZ recommends is a good solution, though it might be too thick and being adhesive backed difficult to press in to the gaps. In the past I've used successfully 15mm filler rod, there is also a 10mm if thats too thick. It simply compresses in to place and create a solid air seal. Then obviously the new skirting will cover it all over.

Regards, Nailbag

jacobm

Thanks @JacobZ, @Nailbag ,

Yeah ive bought some 15mm & 10mm filler rod to do the job, but after inspecting the gap closer, i felt like the rod will just fall through the gap, as there is nothing to actually support it. Expanding foam might be the way to go.

But after reading what i have, im a bit more concerned about the lack of support. The installation manual mentions trimmers are recommended, but more concerningly also mentions that this approach is supported by AS1860.2. Unfortunately i cant find a free version of hte standard to actually confirm it, or see if there are reasonable exceptions (for existing structures, old houses, joist width, etc.)

Screenshot 2024-08-18 193841.png

Nailbag

https://www.workshop.bunnings.com.au/discussion/comment/40982#Comment_40982

Hi @jacobm

If there is a joist within 150mm from the edged opening, I would be happy that you're not going to suffer from the edge of the floor/yeloow tongue bowing or flexing down. So then we are only dealing with the open air gaps. So in this case since you have all ready purchased the foam rods, what I have had to do in situations like yours is to use Sikafill. Run this along both edges of the opening, then gentle press the rod in to place. The sika is quick drying and within 30min the rods will be securely in place.

However, if you can determine what the next closest joist is from the edge, we could advise on whether an end joist should be installed or not. But I have to say, I am disappointed for you that while the floor was up that last supporting joist wasn't installed in the first place.

Regards, Nailbag

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/40982#Comment_40982

Hi @jacobm,

The yellow tongue needs to be supported on all edges as per the installation guide. The tounges or trimmers ensure the boards don't sag between joists. I recommend installing the trimmers between your joists on both sides of the room.

Was it just the pictured sections they missed, or were the trimmers not installed at all?

MItchell

jacobm

https://www.workshop.bunnings.com.au/discussion/comment/82621#Comment_82621

No it was not just this section, it is the whole house perimiter. I will be following up with the installers, so hopefully we can get a positive resolution and fix the issue. thanks

jacobm

https://www.workshop.bunnings.com.au/discussion/comment/82617#Comment_82617

The joists are 450mm apart, running 90 degrees from the wall shown, but there are no trimmers or nogs between the joists at all. Yep im pretty dissapointed myself, a minor job has now been turned into a major one. Thanks

Dave-1

https://www.workshop.bunnings.com.au/discussion/comment/106105#Comment_106105

Evening @jacobm

A pain 😕 But at least you have found it now. I was going to suggest that the plaster and the skirt would cover the edge of the board and stop draughs but you have pointed out an issue I hadnt thought of. Hopefully the installers will fix it.

Dave

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