Building regs query - foundations

Goldie

Registered User
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This is one for those with the technical knowlege of building requlations!

In a situation where there is a raft foundation and 600mm to finished floor level is there a requirement for a sub floor to comply with building regulations?

Would the following build up comply -

300mm Raft foundation
355mm well compacted hardcore
20mm sand blinding
Radon barrier
150mm insulation
Underfloor heating pipes
75mm finished screed

Thanks.
 
a subfloor is a structural element. It is required to take point loads which may occur during the lifespan of a dwelling. The largest point loads may include hot water cylinder, baths, sofas etc... the size of the subfloor can be altered

In your make up, the 75mm screed WILL crack and subside. This may be ok if you upped to somewhere between 100-150mm

PS your hardcore shouldnt be located above your raft.
 
The recommended depth of screed for UFH is 75-85mm, if it is increased to 150mm it will be very inefficient. For load points such as water cylinders it would be possible to build blockwork off the subfloor locally.
 
The usual design of a raft foundation creates the raft itself as a sub floor.

Therefore the 'general' make up is

raft foundation
radon membrane
150mm insulation
1200 guage slipping sheet
UFH pipes
75mm screed with reinforcement


so its possible you have no issue at all.

I have no idea why you are including hardcore and blinding in your specification.
 
You wouldn't put underfloor heating under your tank so why not build a concrete plinth for it when pouring the raft?
 
Syd,

Have a look at my original post and the measurement from top of raft to finished floor. That should explain the use of harcore and blinding. Or am i incorrect in my understanding.
 
there is no requirement for hardcore here, but i see why you are suggesting using it.

i assume the raft was constructed to suit site conditions and to reach 'terra firma'... and now you have to make up 600mm so your floor level matches what you have planning for??

have you priced a T beam and block floor?
 
Syd, yes your assumption is correct. Due to ground conditions we needed a raft and now 'building' up to floor level.

I haven't looked at the t beam system - hadn't come across it previously. My objective is to minimise cost without compromising compliance. My question really is, based on the raft i have and the spec i've outlined would this comply with building regs?
 
Whether it would comply with regs or not I can't say but having looked through the thread again, Syd is right, the screed would crack. I assumed the hardcore was beneath the existing raft. Apart from the beam system, the only other way I would consider would be to construct you base off the raft in the traditional way, i.e.;

blockwork to FFL, then
200mm hardcore
25mm blinding
radon barrier
150mm subfloor
150mm insulation
UFH pipes
75mm screed
 
I am not by any means questioning the replies given to this query (nor am I supporting them - firmly in the no comment camp). I will say this: If you have built a raft foundation ( or any sort of foundation) without design and supervisory input of an engineer ( or architect - though it is really an engineer's area) you are asking for trouble. You may have difficulty getting the property certified compliant. You may therefore have difficulty getting a mortgage. You will certainly have difficulty if you ever want to sell.

Get your engineer on the job.
 
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