Exposed insulated raft foundation

[mike2016]

I'm thinking of building a house in stages over 9 years. I watched Graven Hill grand designs a while back and remember the first house had its foundation destroyed by frost when the underfloor heating pipes expanded. I don't know were they filled and being pressure tested or if this was just by cold air? 

My question is this: is it possible to build an insulated raft foundation and leave it for two years with underfloor heating pipework throughout before adding the timber frame structure (also uninsulated for another year)? Or is it better to wait longer so you can sequence both in the same season? Is there any way to protect the new foundation without the structure or is this too risky? Thanks! 

[Oz07]

I think they put antifreeze in them don't they?

[nod]

We just filled the pipes with and left them pressurized 

[LA3222]

Why not put the pipes in and leave them empty? I didn't pressurise mine for the concrete pour. Dont see the point.

 

The pipes are pressurised. So when you lay them and snip the end you will hear the air woosh out so you know there are no issues while you laid them.

 

During the concrete pour, a pipe loses pressure for whatever reason, what are you going to do. Nothing. You'll finish the slab and have to sort it out later.

 

Some may say pipe need pressurising to expand so that they aren't restricted by the concrete when in use. Really. Just how much will a 16mm plastic pipe expand across its diameter in use at 30 degrees tops. I'd say feck all. 

 

Lay them dry and leave them be?‍♂️

 

 

N.B. I laid mine dry and have the UFH running at 30 degrees, no splits, dents, cracks, corrosion as they say - and no noticeable rise in pressure due to the pipes being strangled by the concrete!

Edited August 21, 2021 by LA3222

[Nickfromwales]

8 hours ago, mike2016 said:

I'm thinking of building a house in stages over 9 years. I watched Graven Hill grand designs a while back and remember the first house had its foundation destroyed by frost when the underfloor heating pipes expanded. I don't know were they filled and being pressure tested or if this was just by cold air? 

My question is this: is it possible to build an insulated raft foundation and leave it for two years with underfloor heating pipework throughout before adding the timber frame structure (also uninsulated for another year)? Or is it better to wait longer so you can sequence both in the same season? Is there any way to protect the new foundation without the structure or is this too risky? Thanks! 

That instance in GH was negligence by the tenacious lady who decided to ignore next door and not add antifreeze. Was a typical example of biting off more than she could chew and moaning about it later. Ignore that, it was the exception not the rule.

If you buy pipes from Wunda, they come sealed at each end and pre-pressurised to a few bar, so as above, if the pipes get damaged during laying you'll ( they'll ) know as the concrete will be blowing bubbles.

The only thing I would be worried about would be vermin / weather attacking the insulation over that extended period of time. I would invest in some shuttering ply ( used / seconds off gumtree etc ) and make a skirt to go around the edge and upstand all the way to ground level and then bench some topsoil / other up against it for the duration. Prob be a good idea to sleeve the UFH pipes or make a similar timber kiosk, with a few breeze blocks around it, to prevent vandalism / UV damage of the UFH pipes. 

 

8 hours ago, mike2016 said:

Or is it better to wait longer so you can sequence both in the same season?

Absolutely the best choice, and no reason not to TBH.

[mike2016]

Thanks all - it's driven by cashflow - paying as I go vs getting a bank to loan me money to do it faster. Talked to self build insurance provider so they won't cover over 24 months so the longer term cash build isn't a runner as far as I can see. Had a massive problem with a major bank so was looking at other options. Also can't get a civil engineer but timber frame provider will let me use theirs but only if I use them! Swings and roundabouts....anyway, appreciate all the feedback and insights. Thanks.