Your thoughts please

[Nic]

Hi attached is the proposal for insulated raft for (passive principle) timber frame build of small new home. 
just getting some general thoughts on it to see if there are any areas which could be improved? Clay based soil and architect changed the original block and beam to this raft .  I’m not a builder or after a passive certificate just want as airtight and thermally sound build on a budget 😁

[JohnMo]

I would

Push the floor insulation to 200mm

And increase the screed to 100mm in fibre reinforced concrete.

Would also have UFH across the whole ground floor, on a single zone (multiple loops).

 

Downside - Your single edge block, would need to increase in height.

 

Then do the whole floor prior to the walls going up.

[G and J]

41 minutes ago, Nic said:

architect changed the original block and beam to this raft

What was the impetus for this change?

[IanR]

2 hours ago, Nic said:

Hi attached is the proposal for insulated raft for (passive principle) timber frame build of small new home. 

 

Not that names matter if you are happy with performance, but I'd not call it an "insulated raft", it looks to me like a standard raft with some thermal bridging mitigation.

 

Have you looked at other Insulated rafts? 

 

Example:

https://www.advancedfoundationtechnologylimited.co.uk/our-products/timber-steel-icf-framed-building-foundation/

 

Where the raft is insulated from below, rather than above, avoiding the need for a seperate screed.

 

How does what has been proposed to you perform? Has anyone calculated psi values?

 

There's no steel shown in the raft, has that been ommitted from the section?

 

What's the wall build up? I assume there are no loads going through the smaller inner sole plate.

Edited August 8 by IanR

[Nic]

I don’t know the answer to those questions but will check 

[IanR]

5 minutes ago, Nic said:

I don’t know the answer to those questions but will check 

While you are asking this questions, try and get a proposed section for a door threshold.

 

General wall to floor thermal bridge doesn't look too bad, but I'd be interested to see what the plan is at thresholds. If there is an issue, it would only be along a short length for standard external doors, but if you have any big sliders or Bi-Folds it may be more of an issue.