suspended floor with larsen truss timber frame to passivhaus high performance

[marmic]

Good afternoons,

 

I have also asked same question on an old post, but thought it worthwhile adding a new one too!   We are using a larsen truss system from Timber Innovations (ie all the load on inner 140mm stud) and have to have suspended floor due to heavy clay, trees, hedges.  We are at passivhaus high performance (won't quite meet certified due to form factor - not huge and single storey). Current plan is preinsulated planks (avoiding screeds etc) with timber frame sitting directly onto edge - so almost replicating a raft, but suspended.  But getting very nervous due to long delays with design (need for coordinated drawings for submission to building control), therefore now urgently exploring other options. Seems to be a few beam & EPS products out there - but how to detail edges with no traditional masonry/brick, where to sit timber frame, and prevent/minimise thermal bridging.  Plus dpc/dpm/ventilation detailing.......... I'm probably not the first one to be doing a lot of head scratching on this topic!  Would appreciate any pointers please... many thanks  kr.........ma

[Alan Ambrose]

Errr, I think we might need a picture/drawing and an indication where you are in the design/build process. What have you decided / designed / built already and exactly which bits still need to be designed?

[marmic]

nothing built.  commence spring once ground dried up!  but need to get ahead...........   extracts of drawings herewith.

1.  timber frame section (ordered) - scribbled bit will be insulation bonded on. May add brick plinth? But probably just insulation as you would with raft and rendered over, or bitumen, or a capping of some sort.

2.  SE foundation design (strip footings) - not final, subject to the design drawings for the insulated precast planks - which are overdue and getting nervous!

3.  strip footings on plan with direction of planks.

[marmic]

just found this which looks reasonably sensible (actually replicating one of my thoughts but hadn't got any further!)   - be interesting to see the other section with beam ends.  and not sure what happens structurally at the sub-floor vents!?

[marmic]

albeit our walls are much thicker, and with timber cladding

[JohnMo]

Although the outer part of the frame isn't structural, would have thought it needs to be supported, not just floated.

 

Pre insulated planks seems complications. If you have to do suspended floor why not block and beam? Add allowance in heights for insulation and screed etc.

 

Just do it thermal bridge free.

 

The 140mm structural bit sounds over kill.

[marmic]

everything on the 140mm.  manufacturers response to question about gap:  We’d expect a circa 10mm gap (for your yellow highlighted section) to the underside of the Larson so it wasn’t loading the brick / insulation cover. This could be closed with a compressible foam (compriband or similar).

 

thermal bridge free - absolutely!  if you've done this would appreciate seeing a detail please?  for increased thickness we'll need to go down as height restriction in relation to adjacent stable block.  hence wondering about beam and eps 

 

Edited February 15 by marmic

[Alan Ambrose]

I would expect your SE (and maybe your architect) should have sweated all the structural / thermal / barrier detail?

[ProDave]

Assuming you are having a masonry underbuild then what you have is similar to us.  Masonry footings, timber floor resting on the sole plate, then a timber ring beam around the perimiter and the timber frame built from that.

 

Easy to detail insulation and air tightness to be seamless between floor and wall.