Hilldes

How to fit acoustic insulation to Posi joists

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Anyone have experience of fitting mineral wool acoustic insulation to metal web/posi joists? How to keep it in place (suspended)? How to get it between the metal webs within a joist? And where do you put it relative to other services?

 

We have 253mm high posi joists at 400mm centres.

 

I'm thinking, from top:

 

1. 22mm Floor deck

2. UFH pipes in spreader plates fixed to the underside of the floor deck using spreader plates.

3. Acoustic insulation - but supported how?

4. All other services - MVHR ducting, cabling, downlights, other plumbing. Will MVHR ducting be noisy if lying directly on plasterboard?

5. Plasterboard

 

P.S. will be using 140mm Frame batts for the acoustic insulation in between the joists as I over-ordered for the timber frame.

 

Any advice/pics greatly appreciated

 

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Posted (edited)

Just push that bad boy in and it will stay. I oversized my cuts slightly by 20mm and then pushed it in.

 

In the metal webs I cut strips the width of the the pozi and threaded it through.

 

Shite job though, even using the knauf stuff I was still itching like a mofo at the end of each day doing it. Horrible.

20210521_161916.jpg

Edited by LA3222

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Use 600 wide rolls and push it between the 400 centres Sitting on the bottom edge 

You don’t need to go in and out of the webbing  

 

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and a wee bit of string or offcut of batten anywhere it wants to be droopy.

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Thanks all. The frame batts I have are for studs at 600mm centres so should be a snug fit. The product I have is Isover frame batts not as itchy as some but not great when working overhead.

 

4 hours ago, nod said:

You don’t need to go in and out of the webbing  

 

 Is that because if you use an oversized width for 600mm centres, it will naturally push into the webs above the bottom chord of the joist? 

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1 hour ago, Hilldes said:

Thanks all. The frame batts I have are for studs at 600mm centres so should be a snug fit. The product I have is Isover frame batts not as itchy as some but not great when working overhead.

 

 Is that because if you use an oversized width for 600mm centres, it will naturally push into the webs above the bottom chord of the joist? 

We do 

Most contractors prefer us to curl either edge up 100 mil

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Question regarding the installation order as I'm not sure.

 

Should the Acoustic insulation be installed before routing electrics and plumbing, or after?

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15 hours ago, crispy_wafer said:

Question regarding the installation order as I'm not sure.

 

Should the Acoustic insulation be installed before routing electrics and plumbing, or after?

I was wondering the same thing. I guess doing the insulation before will hamper first fix electrics and plumbing. Doing it after means installing the insulation over the top of pipes and cables.

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Put the insulation in after first fix mate.  Not an issue with posi joists.

 

Get some decent safety glasses before tackling it too - you really want goggles but they fog up so quick at this time of year!

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7 hours ago, Hilldes said:

I was wondering the same thing. I guess doing the insulation before will hamper first fix electrics and plumbing. Doing it after means installing the insulation over the top of pipes and cables.

Its not going over the top - the insulation will sit underneath it all.

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4 minutes ago, Faz said:

Its not going over the top - the insulation will sit underneath it all.

 

Agree that would be a nice solution. My UFH is to be fitted* to the underside of the floor deck in aluminium spreader plates. I'm thinking the acoustic insulation would be needed immediately below the UFH spreader plates in order to stop the UFH pipes heating the services pipes and cables (and maybe to help focus heat from the UFH pipes upwards). When Wunda specified the spreader plates, they also specified a layer of EPS insulation immediately under the spreader plates, but I omitted this as 100mm of acoustic insulation would do the same thing - provided it was immediately below the spreader plates.

 

* when I say the UFH pipes are to be fitted beneath the floor deck I have not yet tried to thread the pipe through posi joists. From laying the ground floor pipes in the slab, I now know the pipe is like a snake with rigour mortis 😥 (it is the pert-al-pert I think). When we try this in the next few days, it might prove impossible and we'll have to install the UFH pipes on top of the floor deck.

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Well - try it under the bathrooms then. If you do the whole house then your M&E will either rip it out or walk away more than likely.

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5 minutes ago, Hilldes said:

 

Agree that would be a nice solution. My UFH is to be fitted* to the underside of the floor deck in aluminium spreader plates. I'm thinking the acoustic insulation would be needed immediately below the UFH spreader plates in order to stop the UFH pipes heating the services pipes and cables (and maybe to help focus heat from the UFH pipes upwards). When Wunda specified the spreader plates, they also specified a layer of EPS insulation immediately under the spreader plates, but I omitted this as 100mm of acoustic insulation would do the same thing - provided it was immediately below the spreader plates.

 

* when I say the UFH pipes are to be fitted beneath the floor deck I have not yet tried to thread the pipe through posi joists. From laying the ground floor pipes in the slab, I now know the pipe is like a snake with rigour mortis 😥 (it is the pert-al-pert I think). When we try this in the next few days, it might prove impossible and we'll have to install the UFH pipes on top of the floor deck.

I'm afraid to say you have no hope of threading UFH pipe through pozi joists.

 

If you had a small ensuite or summat to do then yeah, at a push. If you have loops 80 to 100m to do there's no hope as you have to keep pulling the entire length through the Web each time. That's a recipie for hating life.

 

I'd lay it over the top. That's what I did tbh, counter battened the floor deck by 32mm, put the pipes down  then threw a pug mix over it all. The only person I know on here that went through pozi joists is @ProDave and he did it for small rooms - he will tell you it was a ball ache!

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Or better yet use a low kW electric mat.

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Posted (edited)
7 minutes ago, Faz said:

Well - try it under the bathrooms then. If you do the whole house then your M&E will either rip it out or walk away more than likely.

I am effectively the M&E consultant and I can't run away 😀

 

7 minutes ago, LA3222 said:

I'd lay it over the top. That's what I did tbh, counter battened the floor deck by 32mm, put the pipes down  then threw a pug mix over it all. The only person I know on here that went through pozi joists is @ProDave and he did it for small rooms - he will tell you it was a ball ache!

Agree its not going to be easy. The main reason for reluctance to install on top of the floor deck is limited headroom on the first floor - but if it just will not work below, we'll install above.

 

 A lesson for anyone placing a contract with a timber frame company, you might ask if they can pause the frame erection while you install spreader plates on the posi joists and lay the UFH pipes, then you discover when they arrive to erect they have manufactured the joists and deck into cassetes.

Edited by Hilldes

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I hope you don't mind a wild suggestion....isn't that we are here for?

I have never done UFH except in concrete floors, so may be wrong....but hoping to learn in time before having to do it to an upper joisted floor

BUT I do like the answer above of putting it on top, assuming you have the headroom....we do not.... and may use big rads upstairs.

 

My off the wall thought.....multi-conditional....is  that if the UFH pipe went parallel to the joists , then only at the ends could there be an issue. IF the joists have plenty of bearing it MIGHT be poss to notch the tops to cross the pipes to the next gap. Only at the ends though , where the stresses are dwindling. Needs approval from floor designer.

You still have to get the pipe to the location too.

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Posted (edited)
11 minutes ago, saveasteading said:

 then only at the ends could there be an issue. IF the joists have plenty of bearing it MIGHT be poss to notch the tops to cross the pipes to the next gap.

The ends are the only bit that are the issue to go through the joist, but you still have to pull 80m of pipe through the first end, maybe 70m of pipe through the next, 60m through the next and so on. Do that for 8 rooms upstairs and it becomes a mammoth task.

 

You can't notch pozi joists. With the best will in the world its not the done thing.

Edited by LA3222
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If your BCO sees 'notched' joists you are going to be in a world of trouble - best not go down that route.  I have the spare ways on the manifold and, looking at all the issues, quickly decided that mats were the way to go.

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41 minutes ago, Hilldes said:

 

Agree that would be a nice solution. My UFH is to be fitted* to the underside of the floor deck in aluminium spreader plates. I'm thinking the acoustic insulation would be needed immediately below the UFH spreader plates in order to stop the UFH pipes heating the services pipes and cables (and maybe to help focus heat from the UFH pipes upwards). When Wunda specified the spreader plates, they also specified a layer of EPS insulation immediately under the spreader plates, but I omitted this as 100mm of acoustic insulation would do the same thing - provided it was immediately below the spreader plates.

 

* when I say the UFH pipes are to be fitted beneath the floor deck I have not yet tried to thread the pipe through posi joists. From laying the ground floor pipes in the slab, I now know the pipe is like a snake with rigour mortis 😥 (it is the pert-al-pert I think). When we try this in the next few days, it might prove impossible and we'll have to install the UFH pipes on top of the floor deck.

 

Top tip - DO NOT thread UFH through the pozi joists, you will struggle to do that without kinking it.

 

We stapled spreader plates down on the pozi joists and laid the 16mm pipe - one bend sat within the gap between pozis and the other sailed over the joist, secured with a pipe clip. As our OSB floor deck was 18mm, we just left a gap where the over joist pipes sat. Protected with a few strips of ply during the build and then the final floor covering (in our case, ply and then resin) covered the whole lot.

 

We did try the threading method initially but gave up after 5 mins when it was clear it would not work.

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13 hours ago, saveasteading said:

My off the wall thought.....multi-conditional....is  that if the UFH pipe went parallel to the joists , then only at the ends could there be an issue. IF the joists have plenty of bearing it MIGHT be poss to notch the tops to cross the pipes to the next gap. Only at the ends though , where the stresses are dwindling. Needs approval from floor designer.

You still have to get the pipe to the location too.

Great idea, but I don't think you can notch the chords of posi joists.

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3 minutes ago, Hilldes said:

Great idea, but I don't think you can notch the chords of posi joists.

exactly

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13 hours ago, Bitpipe said:

Top tip - DO NOT thread UFH through the pozi joists, you will struggle to do that without kinking it

We did try the threading method initially but gave up after 5 mins when it was clear it would not work.

Going to have a play today with some longer pipe offcuts from the slab UFH installation. I know you and others are going to be right.

 

Looking at overfloor, looks like the total additional depth would be 28mm for Wunda:

 

20mm boards:

https://www.wundatrade.co.uk/shop/home/quick-shop/wundatherm-quick-shop/boards-quickshop/underfloor-heating-board-wundatherm-premium/

4mmx2 duo boards:

https://www.wundatrade.co.uk/shop/home/overfloor-retro-fit-solutions/wundatherm-underfloor-heating-boards/7mm-duo-board-system/

 

Besides the headroom issue, may also bring floor level too high to open Juliet doors, but will take a look today.

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I realise notching joists is not to be encouraged....even when it is ok it encourages plumbers and sparkies to cut anywhere they feel like it.   this was only suggested if there happened to be a comfortable overlap of the bearing wall (ie not working past that point0. or if there was an actual gap between end-to-end joists or joist to wall that would allow a turn. ONLY with permission of the joist designer.

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1 hour ago, Hilldes said:

Going to have a play today with some longer pipe offcuts from the slab UFH installation. I know you and others are going to be right.

 

Looking at overfloor, looks like the total additional depth would be 28mm for Wunda:

 

20mm boards:

https://www.wundatrade.co.uk/shop/home/quick-shop/wundatherm-quick-shop/boards-quickshop/underfloor-heating-board-wundatherm-premium/

4mmx2 duo boards:

https://www.wundatrade.co.uk/shop/home/overfloor-retro-fit-solutions/wundatherm-underfloor-heating-boards/7mm-duo-board-system/

 

Besides the headroom issue, may also bring floor level too high to open Juliet doors, but will take a look today.

 

What is your originally proposed floor build up from the joist up?

 

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8 hours ago, Bitpipe said:

 

What is your originally proposed floor build up from the joist up?

 

22mm Caberdeck + (1) underlay and carpet or (2) tiles in bathrooms

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