Green Building Forum - Insulating Suspended Timber Floor, ready for UFH

Insulating Suspended Timber Floor, ready for UFH

sweevo — Wed, 29 Aug 2007 23:08:18 +0100

Hi,

we're (hopefully) soon to have some renovation work start on our home. As part of the work all rooms that are involved will have the floor insulated (100mm K3 Kooltherm) and UFH (Polyplumb overlay) installed. The work does not include the kitchen however which is where the condensing combi boiler is situated.

Our plan was always to rip out the old kitchen (already in place when I moved in 8 years ago) and replace with a new one of our own choice and use this as an ideal time to install the UFH along with the manifold etc in there first. At the moment the floor in there (suspended timber) is not insulated so i'm planning on doing this part of the work myself, ie prior to UFH installation. I'd looked into how to do this about 12-18 months but just wanted to run my plan of action by people who are far more experienced when it comes to this kind of thing.

First up, the K3 Kooltherm is expensive and with the boards being 600mm wide there will be a lot of wastage, ie joists are approx 370mm apart. I was told I couldn't glue spare pieces together to make a new one so I figured i'd be throwing 1/3 of the stuff away which seemed like an awful waste. Because of this I looked at Space Blanket as an alternative. The 200mm rolls have an R Value of 4.5mK/w which if I understand the sums correctly would equate to a U value of 0.22 which is what is specified in the building spec for the 100mm K3 Kooltherm. So in effect I get the same level of insulation for far less cost. One thing that I also wondered about was which way to face the silver coated side of the space blanket. In my loft it faces up so I imagine it would be the reverse under my floor, ie facing down to the ground. Anyone know if this matters either way?

So..... I remember reading about suspending the insulation with netting (nailed to the underside of the joists as support) but have heard that this can sag and reduce the effectiveness of the insulation. With this in mind I wondered if there was any reason I couldn't use the more rigid plastic type fencing (usually green) you get in a roll from garden centers etc to prevent any sagging? I was thinking that wouldn't sag at all if firmly secured to the underside of the joists meaning the 200mm of roll would be slightly compressed into the 175mm joists height and hence touch the floor surface above it.

Finally the UFH install guide says to install the damp proof membrane on top of the flooring prior to laying the overlay boards and piping. I think some people have put this membrane below the floorboards and above the insulation. Would having this membrane over the floorboards rather than under it cause any longterm problems with damp/condensation or do I even need to do both?

Thanks in advance......

Insulating Suspended Timber Floor, ready for UFH

tony — Thu, 30 Aug 2007 08:13:30 +0100

Read the multifoil thread please

I would not do overlay -- take up floor -- insulate -- lay pipes on top of the insulation -- relay floor. Make sure that you are airtight between the rooms and under the floor.

You can use all the small pieces of board insulation! If you dont want them I will have them!

Insulating Suspended Timber Floor, ready for UFH

sweevo — Thu, 30 Aug 2007 09:49:02 +0100

Tony, why do you advise against overlay?

I'll have a look at the multifoil thread when I get time later, but the foil on the space blanket is basically cooking foil over 200m of rockwoll/glass fibre insulation. I was opting for this over regular glassfibre/rockwool insulation due to the glassfibre being enveloped and being far more installer friendly because of it.

I did wonder about using the smaller pieces of K3 but was told that wastage was a fact of life with the 600mm boards. I've even rang the kingspan techline and they say there's no way they recommend to join the boards. I did ask if you could compress two pieces between the joists and they said yes BUT supporting it could be a problem, which makes sense. I've since been looking at Thermasafe styrofoam (PET) insulation. I can get even better R & U values @ 200mm with that so i'm also tempted to go down that route instead.

Insulating Suspended Timber Floor, ready for UFH

tony — Sat, 01 Sep 2007 00:16:54 +0100

sweevo, laying over the floor boards seems wasteful to me, you will also loose some headroom, make it difficult for future maintenance under the floor, it will cost you more, to mention a few of my reasons.

Insulating Suspended Timber Floor, ready for UFH

sweevo — Sun, 02 Sep 2007 10:50:43 +0100

Thanks for the comments Tony. Our ceilings are 2.6m so we're happy to lose approx 23mm due to the install. I'll have a chat with the plumber regds costs though. As for underfloor maintenance, regular UFH would be even harder to take up wouldn't it as the piping is laid in screed between the rafters isn't it?

Insulating Suspended Timber Floor, ready for UFH

tony — Sun, 02 Sep 2007 16:27:39 +0100

No, no need for screed just lay the pipes on the insulation under the floor boards.

I would be more worried about loosing 25mm off the height of the door opening. Already very tall people have to duck through door ways.

Do you have any very tall friends?

Insulating Suspended Timber Floor, ready for UFH

Terry — Sun, 02 Sep 2007 21:52:43 +0100

To follow on from Tony's last comment. A UFH supplier we have spoken to suggests batons fixed to the joists to carry EPS insulation with the UFH pipes fixed to it as per tony's sugestion. They then recommend 20mm screed to level with top of joists to evenly distrubute the heat. This is in place of the diffusion plates used by other suppliers I would imagine?

Insulating Suspended Timber Floor, ready for UFH

tony — Sun, 02 Sep 2007 22:04:58 +0100

Amazing! how will 20 mm of screed evenly distribute the heat? Does not sound very scientific to me or that sensible either.

Insulating Suspended Timber Floor, ready for UFH

Mike George — Sun, 02 Sep 2007 22:52:27 +0100

20mm of sand and cement screed will crack up. The minimum I have seen used is 65mm. It is more sensible to use 75mm with fibre reinforcement, though I do not see the point in any screed at all

Insulating Suspended Timber Floor, ready for UFH

tony — Sun, 02 Sep 2007 23:41:35 +0100

In between wooden floor joists!! never mind the cracks worry about creaks and groans.

Insulating Suspended Timber Floor, ready for UFH

Mike George — Mon, 03 Sep 2007 06:59:24 +0100

Sorry, too much alcohol last night, I did not fully read the thread I assumed we were talking about insulating completely over the top of the joists, which would be just as daft.

Insulating Suspended Timber Floor, ready for UFH

moogaloo — Mon, 03 Sep 2007 14:17:48 +0100

I got lots of quotes for UFH including polyplumb overlay, by far the cheapest was chelmer which is underfloorboards PUR board suspended by battens attached to the joists and pipes attached to the top of the insulation. Heat is then distributed by litag granuals, which if you ever need to get to the subfloor can be hovered up and replaced.

Chelmer was about 1/3 price of the polyplumb overlay, though you do need your boards taken up and relayed.

Insulating Suspended Timber Floor, ready for UFH

Terry — Mon, 03 Sep 2007 22:08:59 +0100

Tony/Mike
had similar questions regarding the screed and will be asking them about it.

Having just read moogaloos comments, checked the Chelmer website and they recommend 'a dry sand and cement' fill around the pipes in some situations?

Insulating Suspended Timber Floor, ready for UFH

moogaloo — Tue, 04 Sep 2007 12:49:41 +0100

Try emailing chelmer and ask them about lytag

Insulating Suspended Timber Floor, ready for UFH

moogaloo — Tue, 04 Sep 2007 12:58:36 +0100

This site has some picks of lytag being used for UFH over PUR board with pipes from chelmer

It is the last third you are interested in

http://www.staff.ncl.ac.uk/roger.broughton/newhouse/miniblog/miniblog.htm

Insulating Suspended Timber Floor, ready for UFH

sweevo — Tue, 04 Sep 2007 22:48:52 +0100

Tony, no need to worry about the door height, there's just over 6' 6" clearance at the minute. The overlay and plywood will reduce this by approx 22mm so it's not really an issue as I don't know any basket ball players.....yet :oD

I've decided to opt for 175mm of thermafleece for the insulation too. Just need to decide on my breather membrane and that's me sorted I guess. Anyone got any recommendations?

Insulating Suspended Timber Floor, ready for UFH

tony — Tue, 04 Sep 2007 23:13:07 +0100

strawberry netting

Insulating Suspended Timber Floor, ready for UFH

sweevo — Tue, 04 Sep 2007 23:38:13 +0100

Sorry Tony, think i'm getting my terminology all mixed up here. I want a membrane to lay over the joists and insulation so that I can also draft proof the floor at the same time. I thought i'd need something like an airtight breather or damp proof membrane for this. There's quite a draft throught the floor in the winter, especially in the kitchen. The ground floor is all suspended timber and the house has air bricks for cross ventilation on all four external walls below it.

I was intending to suspend the insulation using netting unless someone had a better suggestion.

Thanks for all the input by the way. :o)

Insulating Suspended Timber Floor, ready for UFH

tony — Wed, 05 Sep 2007 09:44:04 +0100

I would use polythene not a breather membrane laid over the joists and trapped behind the skirtings.
I dont think it is right to use a breathable membrane on the warm side of the insulation you want no chance of condensation in the insulation.

Insulating Suspended Timber Floor, ready for UFH

sweevo — Wed, 05 Sep 2007 14:29:25 +0100

For simplicity I was thinking of using a 1000 gauge damp proofing membrane from a local hardware store mainly due to the fact that it's dimensions will cover the whole floor in one go with no need for overlaps and joins etc. I'm guessing this in effect is a large polythene sheet but my diy paranoia says i'd better ask before forking out for it. Would this be suitable?

Insulating Suspended Timber Floor, ready for UFH

tony — Wed, 05 Sep 2007 16:37:43 +0100

Yes it is just thick polythene, but so would much thinner polythene

Insulating Suspended Timber Floor, ready for UFH

sweevo — Wed, 05 Sep 2007 22:12:41 +0100

Ok Tony, thanks for sticking with me on this and thanks for all the help and advice. Fingers crossed the work will be starting in earnest in just over a weeks time. I've got a few tradesmen booked in for various bits and pieces with me and my Dad doing the flooring and insulation in between.

Insulating Suspended Timber Floor, ready for UFH

Henry Sears — Wed, 05 Sep 2007 22:26:55 +0100

Posted By: sweevo

I was intending to suspend the insulation using netting unless someone had a better suggestion.

Would it not make the insulation more effective if you used something that stopped air movement across the underside of the insulation, but still allowed any moisture to get out? Maybe geo-textile fabric - it's fairly cheap.