DPM questions?

Hi all,

I am building a sunroom/garage extension on the house and have a couple of questions for those of you have done this before.

Is it ok to double up the DPM (1200 gauge 300ubore)? just to be sure as we are on moderatly damp soil and I want to be really sure I don't perforate it (it is on a 1 inch sand blinding). Couldn't get 2000 gauge.

I want to lay the Kingspan insulation and do some plumbing (for rads etc)

- How do you stop the whole thing from filling with rain water? does it matter? I know the cement slab is going to be damp, but the kingspan boasts non-permeability - is the water just going to sit there? (don't tell me to use a pitch fork to create some drainage holes in the DPM!)

I was talked into of 3 inch kingspan (TF70 - urethane) for the sunroom - I was thinking of 4 inch but the guy in the BM said I was nuts! £36 per 8x4 sheet (need 40sq.mt - rads, ext wall of glass) Am I nuts? (keep answers related to this particular issue!)

Finally - Is it really necessary to have a screed over the slab? I am going to use readymix, so a little bit extra would save a lot of mixing for a 2 inch screed (65sq.mt area). I would take my time on a good finish and if the worst happened I could use a levelling compound? The sunroom will be finished with wood and the garage will be painted.

Thanks for any advice - hopefully further questions will be related to the roof!

Thanks,

Derek.

Reply to
Derek
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Oh My God!! Talk about going overboard...

An inch of blinding? What do you think is going to perforate your 1200 gauge dpm laid over an inch of blinding? You been reading Dune lately?

Don't worry about the rainwater - it'll all go when you're done.

3" kingspan for floor insulation in a sunroom? Much insulation there. The BM buy's opinion was fairly accurate ;-)

As for the screed - no, it isn't neccessary - it all depends how you intend to finish. If you're laying a floating wood floor, or if batten/boarding, you can do this straight onto your slab (which is already sitting on 3" of kingspan, a dpm, 1" of sand, and I would guess

3-4' of hardcore - right?). Take your time and get a good finish on the concrete - it's not that difficult to work it into a really smooth surface. The area is a little on the large side for one person to do in one shot - if you can get a hand from someone else that would really help.
Reply to
Grunff

Does this salesman have your heat loss figures? How does he know? He is going by rule of thumb, which is meaningless. In short calculate it. Anyhow 1" extra is nothing.

If having a wood floor there is no need for a screed.

Reply to
IMM

Ha, ha, true, I suppose it is 1 inch at the thickest. I could only get the wacker plate to get the hardcore reasonably level, I found it much easier to level the sand accurately.

Yeah - I guess I was planning for maximum comfort. I was looking at the product spec last night and his comment "What the f**k do you need that for?" was probably justified. I'll go with the 3", even though the 2" is more than adequate.

Good thinking. I will draft in some family to give a hand.

Thanks,

Derek.

Reply to
Derek

The regulation figures suggest a level of 2" urethane. I am more thinking of comfort and future energy costs.

Thanks. As I thought, but it is good to hear it from others.

Thanks,

Derek.

Reply to
Derek

The regulations figures are the minimum. In other countries they have far higher insulation regulations than us. The insulation regs are being hyped over the next 3 to 4 years, to far higher than the current regs. If 4" is not that expensive, go for it.

Some beam and block floors have 4 to 6" of foam insulation between the beams. 4" is not a lot, and will not be in few years time, so you may as well put it in while you can. You can't easily update it in the future. It is not like laying another layer in the loft.

Reply to
IMM

B&Q will do a 8m x 5m "value" tarpaulin for 10 quid. They are excellent for the money. I have several currently shielding various bits of conservatory from the rain until we actually get five minutes of good weather. Luckily most of it has at least one coat of undercoat (+ preservative primer + ClearChoice pressure treatment), so that should hopefully be enough...

Christian.

Reply to
Christian McArdle

Yes but it won't make it better at stopping damp.

You bail it out before pouring slab.

Buy it from Seconds & Co. for a lot less than that.

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they deliver to the door.

If your insulation is under the slab then you can powerfloat off the slab and aviod the need to screed.

Rick

Reply to
Rick Hughes

Phone your local councils Building Control officer who will tell you the inslation requirements for the floor, then look up the spec for you thickness of insulation (web site, phone company etc.).

You may want to put the DPM on top of the insulation. A builder (I trust) has told me of cases of concrete getting under the insulation and floating it to the top.

Also, make sure folds in the dpm don't have the gaps in the direction which the concrete is poured from or else the concrete may flow into the gaps. Alternatively tape all joints between sheets of dpm.

Neil

Reply to
Niel A. Farrow

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