Can PIR go on top of a timber suspended floor, instead of between?

[scott08]

There's been a bit of a mistake with the bricklayers (long gone) and the height for the bifolds in my extension - essentially just too high. To avoid putting astep in before the door, I'm considering putting PIR over the whole floor, instead of between the joists. This should sort the level height, won't be too damaging on the CH (still at 2.55m after this), and would be way easier to fit. My questions are:

1. Is this a valid way of insulating/ fine for building control?
2. What would the build up be? I will be installing wunda underfloor heating, so imagine it would be 22mm boards, PIR, the wundaboards, then floor covering, but unsure if it needs a second layer of chipboard.
3. Is there anywhere I can find a reliable u value calculation? I can't work out how much insulation is needed, as all the calculators are for insulation between joists.

 

[noseall]

There's been a bit of a mistake with the bricklayers (long gone) and the height for the bifolds in my extension - essentially just too high. To avoid putting astep in before the door, I'm considering putting PIR over the whole floor, instead of between the joists. This should sort the level height, won't be too damaging on the CH (still at 2.55m after this), and would be way easier to fit. My questions are:

1. Is this a valid way of insulating/ fine for building control?
2. What would the build up be? I will be installing wunda underfloor heating, so imagine it would be 22mm boards, PIR, the wundaboards, then floor covering, but unsure if it needs a second layer of chipboard.
3. Is there anywhere I can find a reliable u value calculation? I can't work out how much insulation is needed, as all the calculators are for insulation between joists.

I'm struggling to envisage your scenario. Sorry but it sounds like a joke thread. How on earth could the bricklayers get the DPC or FFL wrong?

 

[Deluks]

A picture would help. It wouldn't be the end of the world to put the brickwork right, and would probably cause less hassle overall than your proposed solution would.

 

[stevie888]

You'll surely have a step at the other end of the room if you follow your cunning plan?

 

[scott08]

I'm struggling to envisage your scenario. Sorry but it sounds like a joke thread. How on earth could the bricklayers get the DPC or FFL wrong?

I don't have the best picture as i'm not on site, but here's the door:

With the current build up, the DPC/ top of the brick that the bifold is sitting on would effectively be about 10mm above FFL. I didn't realise how big the bifold frame would be, so factoring in the levelling, the size of the frame etc, the height from the floor to the top of the bifold rail would be around 110mm. Not the end of the world but not great either. If the opening was set a brick lower, I would only have a 35mm or so lip which would have been fine. If instead of putting pir between the new timber floor joists, I put it on top (like a warm roof), this would mean I have almost a level threshold.

 

[scott08]

A picture would help. It wouldn't be the end of the world to put the brickwork right, and would probably cause less hassle overall than your proposed solution would.

It would definitely be hassle now as bifolds are in.

You'll surely have a step at the other end of the room if you follow your cunning plan?

There is already a step down into this room, as the back of the property is a slightly lower level, so no real issues there. If anything, this would remove the need for the existing step and have it level all the way through.

 

[noseall]

I don't have the best picture as i'm not on site, but here's the door:

View attachment 418842

With the current build up, the DPC/ top of the brick that the bifold is sitting on would effectively be about 10mm above FFL. I didn't realise how big the bifold frame would be, so factoring in the levelling, the size of the frame etc, the height from the floor to the top of the bifold rail would be around 110mm. Not the end of the world but not great either. If the opening was set a brick lower, I would only have a 35mm or so lip which would have been fine. If instead of putting pir between the new timber floor joists, I put it on top (like a warm roof), this would mean I have almost a level threshold.

What im struggling with is why was the DPC/FFL not set at the correct height?
Why is it so much higher than it should be? It means there is potentially damp masonry above floor level. The inner course of bricks should not be visible, rather, these should have been kept at joist seat level and the floor should have dived into the door recess and finished at the threshold.
It all looks very amateurish.

 

[Deluks]

The bi-folds are only held in with screws, get the installers back to whip it out. Then sort the brickwork, then put back, otherwise this will haunt you forever!

 

[Deluks]

What im struggling with is why was the DPC/FFL not set at the correct height?

Cos they were muppets, not that hard to get your head round!

Mah na mah na, do doo do do do.

 

[scott08]

What im struggling with is why was the DPC/FFL not set at the correct height?
Why is it so much higher than it should be? It means there is potentially damp masonry above floor level. The inner course of bricks should not be visible, rather, these should have been kept at joist seat level and the floor should have dived into the door recess and finished at the threshold.
It all looks very amateurish.

Assume error by the bricklayers but they are long gone - not much I can do about it now anyway!

In the picture I sent, the joists go left to right, and are in pockets in the wall, ends wrapped in DPC. I may have gotten the outside DPC level wrong - I think it's the brick level the bifold is sitting on, but i'll be able to check for sure in a few days. If it is, then it appears the DPC level is 10mm too high? I found another pic during construction, which may help figuring out what's going on:

 

[scott08]

The bi-folds are only held in with screws, get the installers back to whip it out. Then sort the brickwork, then put back, otherwise this will haunt you forever!

There is a row of brick soldiers above the bifolds, so I wouldn't be able to do this - I would have to buy a whole new bifold that's taller

 

[Deluks]

There is a row of brick soldiers above the bifolds, so I wouldn't be able to do this - I would have to buy a whole new bifold that's taller

Feeeeeerrrkkkk meeee!
I'm out of ideas.

 

[Deluks]

What you haven't explained, is how you are going to access the room from the existing room. Will you have a step up into the extension?

 

[Deluks]

There is a row of brick soldiers above the bifolds, so I wouldn't be able to do this - I would have to buy a whole new bifold that's taller

Presume a lintel of sorts above this? Take everything out back to the underside of that.

 

[Ivor Windybottom]

There's no problem with insulating over your floorboards then putting another floor on top. It would be just a floating floor. It needs a vapour barrier immediately under your new floorboards.

I'd recommend 22mm chipboard for a floating floor rather than 18mm, so it's stiffer.

But no idea what your Wunda thing is. Check with the manufacturer. Obviously it needs to be on top of the insulation.

More insulation is always better, I don't see what you need to calculate.