# Floor Insulation, UFH, Screed



## BMD (18 Jul 2011)

Can anyone give me some quick advice on floor insulation with respect to screed and UFH. I am using 150mm of floor insulation but want to know if should these boards be stuck together so as to fill the gaps to stop the screed from flowing between the gaps.

If a polyethene sheet is being used, should this be fitted above or below the UFH pipes (reasoning would suggest below but just want to check)?

Finally are there alternatives to using board insulation for the 25mm up-stand insulation around the perimeter?

Thanks


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## BMD (19 Jul 2011)

Two other questions;

1.If the boards are well taped, is there really a need for the sheet of polyethene?

2. If the walls are dry-lined (38mm insulation) to the slab, does this possibly negate the need to the 25mm up-stand?


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## onq (19 Jul 2011)

Any gap in insulation is a fail.

Depends on what the sheet is used for.

Vapour check is to the warm side of the insulation, damp proof membrane to the cold.

I think you need to check your insulation depths.

Depends on what its intended to do.

38mm is grossly inadequate.

(I think)

ONQ.  

[broken link removed]  

All advice on AAM is remote from the situation and cannot be relied upon        as a defence or support - in and of itself - should legal action   be      taken.
Competent legal and building professionals should be asked to advise in        Real Life with rights to inspect and issue reports on the matters   at      hand.


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## BMD (19 Jul 2011)

Thanks ONQ.

Unfortunately, I'm past the stage where I can increase my dry lining above 38mm. 

But perhaps for the other users you could recommend what you would consider to be adequate for floor insulation (upstairs and downstairs) and wall insulation (cavity wall construction)


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## onq (19 Jul 2011)

Your insulation specification is generally quite light.
We used 70mm Thermafloor under the slab and around the edges.

But that was in conjunction with other details.
You need to employ someone to detail and certify your work.
Its not the function of AAM to take the place of competent professionals.

You could consider augmenting with in-cavity insulation and external insulation.
You'll see the difference in your heating bills year one.

ONQ.  

[broken link removed]  

All advice on AAM is remote from the situation and cannot be relied upon         as a defence or support - in and of itself - should legal action    be      taken.
Competent legal and building professionals should be asked to advise in         Real Life with rights to inspect and issue reports on the matters    at      hand.


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## Superman (19 Jul 2011)

Taping the boards is not enough.  If you are using 150mm insulation, presumably it is a PIR/PUR insulation. This requires that the insulation not get in contact with dampness - it loses a lot of its insulating properties if this happens. (Also make sure it is stored in dry place on site etc.). You MUST make sure there is a PVC sheet put directly above the insulation (below the pipes) to prevent any concrete getting in contact with the insulation.

The way to put in the 150mm insulation is to make it up in layers of say 70mm and 80mm - making sure that the joints do not line up (if you understand)

It is not sufficient to merely bring the drylining to the floor.
If you are putting in drylining, you can increase the size of the slab edge insulation significantly - at least 40mm (because there is no weight put on the edge insulation).  See if they have anything bigger (e.g. use the ordinary floor insulation and cut it to fit).


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## BMD (19 Jul 2011)

Thanks for all the responses.

I have cavity wall insulation (obviously) so hopefully my insulation is a little light as opposed to grossly inadequate.

One final question, what is the function of AAM if it isn't to help out fellow users and the general public with questions they may have?


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## onq (19 Jul 2011)

There are some things a competent professional can only advise on when appointed.
This arises from legal liability and because the execution of the detail is as important as its design.
This, working drawings sets contain integrated solutions to the issues arising - its not "paint by numbers".

Therefore, I posted -

_"Its not the function of AAM to take the place of competent professionals."_

This is different from what you posted -

_"...help out fellow users and the general public with questions they may have."_

=================================================================

As regards helping users and the general public - 

I am the author of the Self Build FAQ stickied at the top of this forum.
I am also the author of nearly 3,000 posts on a wide variety of subjects.
That doesn't mean I see AAM as a means of replacing a professional on a job.

So I don't know how well insulated your cavity is or even of the insulation will work.
That is because vented cavity insulation has one set of problems and full fill another.

=================================================================

Not all architects will agree on the same exact things, but all are competent to advise.
Its important you get an insulated integrated solution from a single source.
You cannot detail a dwelling for compliance in a piecemeal fashion.

Superman for example prefers not to let certain kinds of insulation get with with the pour.
ICF takes a different view of the insulation used in that technology where no lining occurs and the insulation is the shuttering for the pour.

I prefer not to seal moisture in and assume that the heat of crystallization will help dry out HD insulation and the heating of the space will deal with the rest.
Joe Little has offered empirical data on the use of variable vapour checks to reduce the build up of moisture in insulation where a foil vapour check has been used.

What a layperson should not try and do is to cherrypick solutions for different kinds of building elements.
The details of transitions are as important as the close fitting, fixing and sealing of the insulation.
And a body of details are intended to work as a whole for a particular form of construction.

However its your call - I can only offer advice to a certain level on AAM.
But I wrote my disclaimer below partly for the reasons outlined above.

ONQ.  

[broken link removed]  

All advice on AAM is remote from the situation and cannot be relied upon          as a defence or support - in and of itself - should legal  action    be      taken.
Competent legal and building professionals should be asked to advise in          Real Life with rights to inspect and issue reports on the  matters    at      hand.


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## BMD (19 Jul 2011)

Fair enough...worthy points and all well made.

Again, thanks to everyone on AAM for their advice


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## onq (19 Jul 2011)

You're welcome BMD.

The essence of it is - I fear to say too much.
I know that seems hard to believe looking at one of my longer posts, but qualifying the advice given and rounding it out to a certain level is what makes up the post.
It took me five years of study, with over a years spent working on building sites and at least three years post graduate experience at a wide variety of jobs to become what I would class as "competent".

These days I have to constantly run to stand still, reading and digesting new Building Regulations, so-called "approved details" that only deal with sealing and insulation, and new building practices several of which leave a lot to be desired IMO. 

I'm wary of advising in detail over an internet connection - there are too many unknowns and too much rests on detail design, turning corners and angles, services penetrations, radon gas boxes and close fitting of elements. All good stuff, necessary stuff, impossible to do remotely stuff.

That's where I'm coming from - thanks for understanding.

ONQ.  

[broken link removed]  

All advice on AAM is remote from the situation and cannot be relied upon           as a defence or support - in and of itself - should legal   action    be      taken.
Competent legal and building professionals should be asked to advise in           Real Life with rights to inspect and issue reports on the   matters    at      hand


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