Suspended Floor PIR Insulation Support Option

[mattwaddy]

So after lifting floor boards I've found that my joists for suspended floor (ground floor) are 100mm deep. I'm planning to lay wet UFH using a structural board later on, so want to maximise the depth of PIR into the gap between joists. Building control have already been around and are happy with the approach and that I can't do more than the 100mm / 75mm worst case. My question is really what's going to be the best way to support the PIR underneath to get 100mm in. I've seen a post previously that suggested using an Anglebead for plastering at the bottom of the joists and then using the full depth rather than timber battens on the inside of the joist which would mean I have to drop back to 75mm. The only other option I guess would be to apply support battens underneath for the PIR to sit on, so running the opposite direction every so often under the joists, however the gap isn't huge underneath so fixing those in place might be tricky. Now I'm sure a number of people have done this, so just looking for some advice before I start the job next week. Thanks!

 

[freddiemercurystwin]

You could pop some nails into the joists about 1/2 inch above the bottom of the joists, push the insulation down so the nails embed into the insulation a tad.

 

[mattwaddy]

You could pop some nails into the joists about 1/2 inch above the bottom of the joists, push the insulation down so the nails embed into the insulation a tad.

Thanks, I don't think building control approve of that approach any more as it's not as robust but I can check, thanks.

 

[conny]

Cut your battens to the correct width and hammer in the nails/screw in the screws so they just protrude the other side.
Hold the batten in position under the joist and hammer/screw into place. This way you are not trying to hold a batten in place and a nail/screw in position whilst you use your free hand to knock/screw them in. Then simply pack your boards in between the joists to rest on the battens.
Basically, a form of sub-assembly before final fix.

 

[mattwaddy]

I like

Cut your battens to the correct width and hammer in the nails/screw in the screws so they just protrude the other side.
Hold the batten in position under the joist and hammer/screw into place. This way you are not trying to hold a batten in place and a nail/screw in position whilst you use your free hand to knock/screw them in. Then simply pack your boards in between the joists to rest on the battens.
Basically, a form of sub-assembly before final fix.

Sounds like a good idea, not sure there is enough room to be able to hammer them in or screw from the underside still, but maybe a right angle fitment on my cordless screwdriver might work. I'll have a play tomorrow to see if there is space. I guess roofing battens or similar would do the trick. might be able to run larger pieces the whole width underneath rather than cut to the width of each joist pair too?

 

[Mr Chibs]

What about cheapo angle brackets?

angle brackets

 

[conny]

Good idea about the full length battens but you may need to lay them on the ground underneath because, once you start fixing them, you will reduce the gaps to get them in. To nail them you can always turn your hammer side on and use the face of the head or, as you say, fit a right angled chuck in your drill.
Good idea from Mr Chibbs as well. You can pick up angle brackets dirt cheap from the likes of Aldi.

 

[mattwaddy]

What about cheapo angle brackets?

angle brackets

Yeah another good option potentially, I'd assume the PIR would slide over into situ without too much issue

 

[Mr Chibs]

Just try to be as meticulous as possible when it comes to sealing gaps etc, I would use aluminium duct tape to seal all the joints too.
The PIR will just slide over the side brackets.

Good luck

 

[JayP1]

Yeah another good option potentially, I'd assume the PIR would slide over into situ without too much issue

Hi mate, thinking about doing the same thing but putting in 75mm celotex and leave 25mm for pipe and biscuit mix. How did you get on? Do you use angle brackets?

 

[damessiahuk]

Also keen to explore this. I'd love to support from underneath if possible to maximise PIR, and also give me a bit more comfort re strength as could use bigger battens.

 

[Deluks]

Use aluminium roof soakers, screwed or nailed in level with the bottom of the joist.