Floor Screed Questions

Dromardabu

hi all
looking for some advice. We have our foundations laid to sub floor level and the grounds contractor wants to put the insulation and under floor heating down now to finish it off before our timber frame arrives. We are putting 150 mm on the downstaires with UFH but i wondered did anyone know if concrete did the same job as flo screed or the likes in such a circumstance. I wanted to get a liquid screed onto the UHF but this would normally be done when the hosue goes up. Does it make any difference to the thermal conductivity to have a light liquid concrete as opposed to a proper flo screed. Or can floorscreed to done without a house surrounding it. I dont want to make a mistake that i'll have to live with for the rest of my life.
Any advise or guidance would be appreciated.
Ps. the foundations are raft and not insulated. I know we;d have to put down a radon barrier too but wondered was it better to do it now when the floor is open or wait till i have the frame up?

Dromardabu

Dromardabu wrote: »

hi all
looking for some advice. We have our foundations laid to sub floor level and the grounds contractor wants to put the insulation and under floor heating down now to finish it off before our timber frame arrives. We are putting 150 mm on the downstaires with UFH but i wondered did anyone know if concrete did the same job as flo screed or the likes in such a circumstance. I wanted to get a liquid screed onto the UHF but this would normally be done when the hosue goes up. Does it make any difference to the thermal conductivity to have a light liquid concrete as opposed to a proper flo screed. Or can floorscreed to done without a house surrounding it. I dont want to make a mistake that i'll have to live with for the rest of my life.
Any advise or guidance would be appreciated.
Ps. the foundations are raft and not insulated. I know we;d have to put down a radon barrier too but wondered was it better to do it now when the floor is open or wait till i have the frame up?

Anyone ????? :rolleyes:

Poor Uncle Tom

Dromardabu wrote: »

We have our foundations laid to sub floor level and the grounds contractor wants to put the insulation and under floor heating down now to finish it off before our timber frame arrives. We are putting 150 mm on the downstaires with UFH but i wondered did anyone know if concrete did the same job as flo screed or the likes in such a circumstance.

I'm not sure if the 150mm you mention is insulation or concrete. If it's concrete it's way too thick to act effectively for UFH, imo.
The liquid screed you mention is a liquid concrete screed. The only difference between the thin screed and the deeper dryer screed is that the thinner one usually has fibre in the mix for reinforcement.

Dromardabu wrote: »

I wanted to get a liquid screed onto the UHF but this would normally be done when the hosue goes up. Does it make any difference to the thermal conductivity to have a light liquid concrete as opposed to a proper flo screed.

You're talking about the same thing, imo.

Dromardabu wrote: »

Or can floorscreed to done without a house surrounding it. I dont want to make a mistake that i'll have to live with for the rest of my life.

Putting the UFH piping in place at the start rather than the finish of the job has two problems,
1. the pipes have to be charged and left in place until the house is completed, usually over a winter period, if the pressurisation liquid does not contain an antifreeze all the UFH pipework could be ruined.
2. putting all the UFH pipework in at the start means there is no room for tweaking where anything goes at the end, eg., island or fitted presses in the kitchen, units in the utility, etc.

Dromardabu wrote: »

the foundations are raft and not insulated. I know we;d have to put down a radon barrier too but wondered was it better to do it now when the floor is open or wait till i have the frame up?

The radon barrier is a complete membrane laid over the entire area of the floor, this can't be done after the frame has been erected.

These are really elementary questions which should be asked of the supervising architect/engineer/arch tech and no builder should erect a timber frame without having a radon barrier in place, but if they're only being employed from floor level you never know.

BryanF

Dromardabu wrote: »

I know we;d have to put down a radon barrier too but wondered was it better to do it now when the floor is open or wait till i have the frame up?

please employ an architect/arch tech or eng before you make some major costly mistakes

Dromardabu

Hi Uncle Tom
THanks for coming back with your replies. Much appreciated.

Poor Uncle Tom wrote: »

I'm not sure if the 150mm you mention is insulation or concrete. If it's concrete it's way too thick to act effectively for UFH, imo.

I meant that we were putting down 150mm of insulation on the floor with a 50-75mm screed on top.

Poor Uncle Tom wrote: »

The liquid screed you mention is a liquid concrete screed. The only difference between the thin screed and the deeper dryer screed is that the thinner one usually has fibre in the mix for reinforcement.
You're talking about the same thing, imo.
Putting the UFH piping in place at the start rather than the finish of the job has two problems,
1. the pipes have to be charged and left in place until the house is completed, usually over a winter period, if the pressurisation liquid does not contain an antifreeze all the UFH pipework could be ruined.

- good point and worth considering - we would be doing it in the next 3 weeks though so my chances of frost are reducded but it did happen to a mate of mine so i take the point on board.

Poor Uncle Tom wrote: »

2. putting all the UFH pipework in at the start means there is no room for tweaking where anything goes at the end, eg., island or fitted presses in the kitchen, units in the utility, etc.

Granted that was something i hadnt thought of alright - thanks.

Poor Uncle Tom wrote: »

The radon barrier is a complete membrane laid over the entire area of the floor, this can't be done after the frame has been erected.

I was under the impression it was laid on the subfloor with the insulation - then a layer of polythine to stop leakage down between insulation boards and then ontop of that lot went the piping for UFH. The final parimeter layer of insulation around the walls then at 25mm dept to eliminate cold bridging to the exterior. If we lay the radon barrier and the frame is erected on top isnt there a danger of ripping it to shreeds - or how is this normally done ? any advice would be appreciated.

Poor Uncle Tom wrote: »

These are really elementary questions which should be asked of the supervising architect/engineer/arch tech and no builder should erect a timber frame without having a radon barrier in place, but if they're only being employed from floor level you never know.

Agree with the sentiment in the above statement - we do have a supervising engineer who will advise but like all engineers he thinks with the numbers and not neccessaryly about the end product and what its going to me like to live in . . . but thats my issue in fairness.

Thanks again.

Dromardabu

BE_MIEI

There appears to be no coherent design in place with this build (and obviously no supervising professional involved). If this build continues it will most likely be an uninsurable disaster.

Dromardabu

BE_MIEI wrote: »

There appears to be no coherent design in place with this build (and obviously no supervising professional involved). If this build continues it will most likely be an uninsurable disaster.

Hi BE_MIEI
to which post are you referring ?

Dromardabu

BryanF wrote: »

please employ an architect/arch tech or eng before you make some major costly mistakes

Hi BryanF
I appreciate your advice and I do have an architect and a chartered engineer in place. I was simply enquiring for my own information so that i could make an informed decision because ultimately in a self build it falls to me to decide.

Poor Uncle Tom

Dromardabu wrote: »

we would be doing it in the next 3 weeks though so my chances of frost are reducded but it did happen to a mate of mine so i take the point on board.

this means you would have the UFH pipes in place at the end of August, we could get frost in Oct/Nov, will you have the rest of the house completed by then? It's very doubtfull.

Dromardabu wrote: »

I was under the impression it was laid on the subfloor with the insulation - then a layer of polythine to stop leakage down between insulation boards and then ontop of that lot went the piping for UFH. The final parimeter layer of insulation around the walls then at 25mm dept to eliminate cold bridging to the exterior. If we lay the radon barrier and the frame is erected on top isnt there a danger of ripping it to shreeds - or how is this normally done ?

What I meant was that the Radon barrier is positioned underneath the timber frame, not directly in contact with it, but below the level of the frame, not above the frame level as it can't get a complete cover if it is interrupted by the frame's sole plates. The usual position for the radon barrier is on top of the blinded hardcore and below the insulation.

Dromardabu wrote: »

Agree with the sentiment in the above statement - we do have a supervising engineer who will advise but like all engineers he thinks with the numbers and not neccessaryly about the end product and what its going to me like to live in . . . but thats my issue in fairness.

Good, then any questions you have ask away....:)

Dromardabu

Poor Uncle Tom wrote: »

this means you would have the UFH pipes in place at the end of August, we could get frost in Oct/Nov, will you have the rest of the house completed by then? It's very doubtfull.


What I meant was that the Radon barrier is positioned underneath the timber frame, not directly in contact with it, but below the level of the frame, not above the frame level as it can't get a complete cover if it is interrupted by the frame's sole plates. The usual position for the radon barrier is on top of the blinded hardcore and below the insulation.

Good, then any questions you have ask away....:)

thanks for the replys uncle tom.
I knew the radon barrier needed to go under the frame but my fear is that it will get ripped between the time its laid and the time we are ready to put the insulation and UFH down. Its not a major issue just wondered did anyone have a brainwave on how to prevent this. Our foundations are to subfloor level so its time to put the radon barrier down prior to the TF arriving.
If we did put the UHF down now after pressure testing we'd obviously have to blow it our fully to avoid any risk of frost damage however likely . ..

thanks again,
Dromardabu

Poor Uncle Tom

I have moved some posts to a new thread of their own.

Outkast_IRE

Easy soloution is to pressurise the underfloor with air , to a suitable pressure.
This is the method i have used the last few winters and its great for ease of mind if the build is goin on during the winter.

Poor Uncle Tom

Dromardabu wrote: »

I knew the radon barrier needed to go under the frame but my fear is that it will get ripped between the time its laid and the time we are ready to put the insulation and UFH down. Its not a major issue just wondered did anyone have a brainwave on how to prevent this. Our foundations are to subfloor level so its time to put the radon barrier down prior to the TF arriving.

What's stopping you putting the radon down now and putting a a screed on top to protect it, the frame could go on top of the screed.

Dromardabu wrote: »

If we did put the UHF down now after pressure testing we'd obviously have to blow it our fully to avoid any risk of frost damage however likely . ..

Or pressure test it with liquid containing antifreeze (like the solar tubes)

Dromardabu

Poor Uncle Tom wrote: »

What's stopping you putting the radon down now and putting a a screed on top to protect it, the frame could go on top of the screed.
Or pressure test it with liquid containing antifreeze (like the solar tubes)

Thanks Uncle Tom
I was trying to eliminate the need for a second screed over the radon barrier to protect it and do it all together. It could be done that way alright.
The Frame will be sitting on soapbars on their edge and they will form the basis of the soleplate from the frame. The dept on the inside of these is what i want to fill with the radon barrier, insulation, polyethine and then the UHF pipes followed by the liquid screed.
I guess i will just have to complete the floor screed including all the above elements directly after the frame is erected.

cheers

Dromardabu

Outkast_IRE wrote: »

Easy soloution is to pressurise the underfloor with air , to a suitable pressure.
This is the method i have used the last few winters and its great for ease of mind if the build is goin on during the winter.

Cheers Outkast_IRE - thats helpful to know - cheers