Under Screed Insulation - Do's & Don'ts

YourAverageJoe

Just wondering if anyone has any do's or don'ts about laying insulation under an underfloor screed.

muffler

Separate the screed and insulation with 500 gauge polythene - prevents chemical interaction.

Poor Uncle Tom

And a very obvious one, make sure the screed is reinforced.

sinnerboy

Remember - if using UFH - min U Value is 0.15

sydthebeat

sinnerboy wrote: »

Remember - if using UFH - min U Value is 0.15

just to continue this... your probably looking at about 120-140mm polyurethane insulation (get the figures checked!)

the best way to do this is to double up the boards ie 2 x 60mm or 2x 70mm sheets.
Stagger the joints on the upper layer, cut tight!!

Technophobe

....and dont forget the perimeter insulation;)

soldsold

sinnerboy wrote: »

Remember - if using UFH - min U Value is 0.15

I must remember this, I have heard a lot of people saying they are putting in underfloor heating with very little insulation planned under the floor, and 25mm edge insulation.

Staggering the joints in the underfloor insulation is also very good advice, in my case I used 3 layers of 100mm EPS, all joints staggered, 100mm edge insulation with a bevelled top so that the edge insulation is about 30mm wide at the top, 100mm wide about half way down, and 100mm wide all the way to the bottom, and it looks like a concrete paving kerb in side profile.

FergusD

Something else I discovered today to my cost - for at least some self levelling screeds, the house has to be weather tight. We were going to get the floor in while we were waiting on Windows which I've just been told is a total no-no. They want windows in and all slates on before they'll pour.

Fergus.

Poor Uncle Tom

Poor Uncle Tom wrote: »

And a very obvious one, make sure the screed is reinforced.

Ia this a joke? Reinforced with what??

One thing I will say about this is try and minimize people walking on the floor insulation when it is placed. Also ensure the subfloor is super clean before laying the insulation. (use an industrial hoover if you can) Any dirt debris or lumps from plastering or blocklaying on the floor can penetrate the foil underneath the insulation

mickdw

I like to break the screed at the internal doors to stop cracking as it dries