is 80mm too much underfloor

sculptor

I'm laying a 20 m2 floor tomorrow,
hardcore
sand
radon barrier
80mm insulation
visqueen
mesh
ufh pipes
75mm screed
Is the insulation rigid enough?
Do I need to prop the mesh and with what?
Do I need to tape the insulation if there is a polythene sheet between it and the screed?

sinnerboy

sculptor wrote: »

I'm laying a 20 m2 floor tomorrow,
hardcore
sand
radon barrier
80mm insulation
visqueen
mesh
ufh pipes
75mm screed
Is the insulation rigid enough?
Do I need to prop the mesh and with what?
Do I need to tape the insulation if there is a polythene sheet between it and the screed?

i assume you mean

hardcore
sand
radon barrier
150 concrete
80mm insulation
visqueen
mesh
ufh pipes
75mm screed


amount of insulation depends of area/perimter ratio
2007 regs require min u value of 0.15

a usually safe "rule of thumb" is 120 of polyuerethene
best laid in 2 x 60 layers cos a 120 board can develep a curl
if you already have purchased 80 boards order same qty of 40

wet sand cement screed can attack the polyurerthene so best to place 500 gauge polythene over before screed. no need to tape boards if you use polythene

if doing it yourself you will find it easier to lay pipes into purpose made pvc restrainig clip/tracks

sculptor

Thanks Sinnerboy, I have tracks but they are the spike in type will they not compromise the polythene barrier? and where does the mesh go if I'm using tracks, over the pipes?

sinnerboy

the polythene in this position is not like a damp proof membrane .it is simply used to prevent direct contact between the screed and polyuretahne . it is a "belt and braces" measure ie. some choose not to use one , kingspan say "advisable , not essential "

the screed over it should be fairly stiff , not too sloppy ( not like an easi screed)

so occasional puncturing will not prevent the the polythene from protecting the the insulation

once the screed is dried out - you can even remove the polythene ( just kidding !!! ) .

don't think you need mesh too . but if your engineer has spec'd it then place it over the pipes - double check this with your engineer

mesh is often used in lieu of the pvc tracks but it is more hassly to tie the pipes to it compared to using the pvc tracks

con1982

The screed mesh is normally specificied by the Architect or specialist contractor, in the case of easi-screed or similar.

I have seen A142 used in the past.

Conor

NickTellis

Does anyone have any experience with this for use with underfloor heating? It makes sense that the thinner the screed the quicker the floor heats up.

http://www.easyscreed.ie/_easyScreed/easyScreed.html

camroc76

The thinner the floor screed the more likely it is to crack (unless it is defined as being non-shrink). The dpm is also essential in my opinion, it reduces the friction between the two surfaces and therefore prevents a build up of stresses within the screed and as a result prevents cracks when it contracts when it starts to dry out.

NickTellis

Well they say it's non-shrink and 35 mm is recommended for UH. It doesn't even use sand or cement and having looked a video of how it's mixed it appears to use some sort of plasticiser. Sounds perfect for UH.

bauderline

Yeah, the idea of easyscreed is that you can get away with the thinner layer 35mm of screed.

Its has pros and cons though, with UFH your floor kind of acts like one giant storage radiator, the thinner the screed the more quickly it will heat up, but also it will also cool more quickly.

The normal 75mm screed takes longer to heat up, however it will retain and "give out" heat for a longer period of time. You need to consider your options carefully as if you are using GeoTherm you will want to run the heat pump mainly using off peak electric.

I am not convinced oil works well with UFH and gas is getting kinda pricey... another consideration for you....

That's my AFAIK anyway....

Baud.

NickTellis

A very good point Baud but personally I think I'd prefer to have the UH "on-demand" (well as on-demand as UH gets) rather than having to wait a few hours for it to heat up sufficiently. I was thinking in terms of using this screed in conjunction with a pellet boiler / buffer tank.

sinnerboy

Baud is correct .

Yeah , i've used it twice- happy clients delighted with fast response . Both cases using standard efficiency gas boilers to Ground floor , rads to first floor ( sorry Syd )

Contractors loved it - effortless flat floor .

BE AWARE

- it is no good for wet room areas
- it has poor mechanical strength - ie. do it too soon in the build and it may break down under workman's boots / decorators trellis etc .