ADLIan

Flat roof definition of up to 10 degrees is in a number of British Standards on roofing.

Look very carefully at your detail - there are a couple of timber elements missing that are needed to make this detail 'buildable' and they will impact the psi-value. Also regarding the general detailing of an I-joist corner - is your detail from an approved source/manufacturer? I'm thinking more from a structural connection perspective here. I do not know how psiclops works so cannot comment if the above are down to user input or how psicops handles the data.

'Cavity barriers' and 'fire stopping' are totally different items and are noted as such in Appr Doc B. Fire stopping is normally related to compartment walls and floors found in blocks of flats, semi detached and terraced houses. Even the BCO is confused!

Just a couple of comments on the attachment after a quick look through. Standard external temp is normally 0 Deg C rather than -5 though this probably makes no difference. Also there are timber elements missing from the junction detail.

So nothing stopping manufacturers (block, insulation etc, etc) generated psi-values being used. Until recently I was Elmhurst accredited so know the process, been through the program, trained in 2D & 3D calcs along with consultancy for insulation manufacturers. If I received a set of psi-values from a self builder and random website I'd be back to using the SAP defaults to protect myself. Manufacturers have normally invested in their technical people to undertake these calculations. Sorry Robin but please check SAP and supporting documents for thermal bridging.

The floor edges are dealt with as a linear thermal bridge separate from the insulation (& Uvalue) in the general floor area. The ground floor/wall junction is a difficult one when preventing/minimising the thermal bridge. This is more difficult with a suspended concrete slab that bears on inner masonry - 'overlapping' the cavity wall and floor insulation is one option. This is further complicated with beam and block. Relatively simple where the beams run parallel to the wall (2D thermal analysis) but probably requiring a 3D thermal analysis where the beams run into and bear on the wall. Again extending any cavity insulation to well below the floor insulation will help.

I still cannot find where SAP 10.3 does not allow manufacturer psi-values. Is there another guidance doc that you are referring to? Can you please post here?

Agree with comments re the OP. If the FEM Uvalue of an I-joist wall is so much better than that from the BS EN 6946 method I would suggest one result is incorrect. The combined method gives accurate results provided the I joists are modelled correctly. Therm output is not very intuitive!! I’ve used both methods on a wide range of wall details and they tend to agree. A quick read of SAP 10.2 and 10.3 appears to have identical guidance on dealing with linear thermal bridges. Where do you see any differences?

Do you already have Building Reg approval for this house? SAP 10.3 is in support of the next Appr Doc L1 (2026) effective from March next year. Using both SAP 10.2 and SAP 10.3 is just extra work for no real benefit. As I understand it both versions deal with linear thermal bridges in the same manner and manufacturers of insulation/blocks/TF etc (as competent persons) the psi-values are acceptable. Not much background info on who or what is behind psiclops - tread carefully!

I don't understand how this is suddenly an issue now the work is underway as this should have been sorted as part of the design stage SAP calculation and your Building Reg application. Has the SAP assessor taken the lazy option and used the default (worst case) thermal bridge numbers? Most insulation, block & lintel manufacturers have their own sets of psi-values that can be used and these will be a lot better than the default values. The TF manufacturer/designer should also have bespoke psi-values. Producing bespoke psi-values is very time consuming - if there are a lot of junctions to assess costs could easily be £2k plus!

Do not confuse wood wool and wood fibre boards - they are very different materials.

Please do not omit the fixing(s) - it's only one or 2 per board (check MIs). In a fire any plastic insulation attached to the plasterboard will melt or soften and the plasterboard may fall off the wall. This exposes more fuel to a fire (combustible insulation) and blocks possible escape routes. Additionally it could be a major hazard for fire fighters if they have to enter the building if people reported in there.

I believe approved contractors (to PAS????) can self certify

I’m sure PUR is ok for with render. Does this product have a foil face? This may be the problem as render will not stick, product for direct render normally has a glass tissue facing

Ask him what part of Approved Doc H (assuming England) applies. New one to me.