ADLIan

@ProDave Is this wall 'standard' timber frame? - the calculation does not appear to account for the thermal bridging of the timber studs. The default is 15% bridging and this would increase U-Val nearer to 0.15 W/m2K. Also there is a layer of '25mm spruce' - seems strange to have an inch of solid timber at this point! Should it be 25mm air space & batten.

Polyurethane & polystyrene foams have no acoustic properties. Must be mineral wool, glas or rock.

Have a chat with the insulation manufacturer on Monday morning. Their technical services will do the number crunching for you and send a nice pdf print out that BCO will accept. Ian

You could try CIGA the cavity wall insualtion guarantee people, www.ciga.co.uk.. If regisitered they will have details of the job and any guarantee. Heard mixed reports of how they handle compliants!! Ian

Thanks Crofter Ian

Interesting discussion guys Can someone (ProDave?) point me to the reference exempting portable buildings upto 100m2 from building regs/building warrant? Thanks in advance.

@Barney12 Lots of information missing from the linked spreadsheet, it barely scratches the surface of the required input data!! An accredited asssessor should not accept the input data from any 3rd parrty - not even another accreedited assessor. Any errors are then yours and continued accreditation may be at risk. Personaly I value my professional reputation, status and accreditation too much to risk this course of action. A good asssessor will not just do the number crunching but will also offer independant advice and guide you through the myriad of options available under SAP. I use NHER Plan Assessor and find it a great bit of software. Elmhurst is good too just takes ttime getting used to sometihng different. Ian

Difficult to say if the numbers are making sense without knowing the raw input data in detail. Unless you are very good with Excel and understand the complexities of SAP in great depth I wouldn't bother compiling my own spreadsheet!! Also remember that SAP software should be BRE approved - this ensures all software from all suppliers is churning out the same results. Without some form of checking against recognised sofware your spreadsheet may be giving meaningless numbers. Software, even free trial versions, from the major approval bodies should give a warning if wrong info is used - if you are getting erroneous figures either the software is not up to scratch of you need to study the SAP document in more detail - insomnia cured!! Ian

If its saturated I would suggest replacing it. Perhaps best if you contact Rockwool for their comments. Ian

Hi Info on SAP (new build houses) and rdSAP (existing houses) is available from the BRE website - full SAP/rdSAP guide and conventions for both schemes can be downloaded. Re SAP ratings - this is based on fuel cost so choice of fuel will have a big impact as will space/water heating system efficiency. Fuel costs are given in Table 12 of SAP 2012. Ian

The SAP rating is based on energy cost and is relatively insensitive to insulation levels but very sensitive to fuel type & price. Typically if a mains gas powered house has SAP in the low 80s expect same house to be mid 70s (ish) if using bulk LPG or ASHP. But latter 2 will give higher CO2 emission (though off set by high efficiency of electric ASHP). +1 Declan - it's the CO2 emissions and fabric energy efficiency standard the BCO will be looking at.

VCL should be on inside of panel. Breather membrane is external to panel.

District heating system pipework. Ian

The solutions shown in the Regs for partition floors and walls within a dwelling are deemed to satisfy the requirements - so BC will not ask for test in this instance. For separating floors and walls between dwellings/flats the options are testing on completion or using the Robust Details scheme.

Yep. Acoustic performance, same as thermal, depends critically upon detailing and workmanship. The smallest of gaps or imperfections in the system will allow sound through and degrade the performance of the floor or wall.

@TerryE - I think you've answered your own question as to why acoustic insulation is required in floors (& walls) within dwellings! Part E was improved considerably back in 2003/4 as a direct result of public concerns about the (poor) qualiity of acoustic insulation both between and within dwellings. Ian

The resilient bars are often used as part of the acoustic solution in separating floors i.e between dwellings/flats. Also often used if higher acoustic performance required. In partition floors within a dwelling the 100mm mineral wool quilt is the option to comply with Regs. Ian

Not meaning to be negative just trying to advise on accepted good practice within the timber frame and insulation industries backed by British Standards and BRE work. if you are happy with the system and your BCO is willing to sign off then fine. Ian

PeterW - problem with blown bead (or fibre) is you never know if the cavity is filled correctly and without voids - the estimate of product usage and target installed density is VERY approximate. This may be OK with refurb where anything is better than nothng but not, in my view, in new build. At least with a built in product you can see if it's installed correctly or not! Ian

Hi ProDave It's not just BC sign off - the wall has got to last long after your BC has lost interest. The recomendation from TRADA etc is there for a reason. From past experience they note this type of system causes problems in the longer term - if you are happy to accept this risk then fine. I note that a woodfibre product, Diffutherm, had BBA certification for your exact application but it has now lapsed or been withdrawn. Ian

Sorry been awol on trans atlantic flight! Nice pic Jack. I've seen similar with polyurethane and gaps of several cm between the slabs! Back to the main topic. Generally no need to vent the cavity on standard masonry cavity or TF with brick/block cladding (though weep holes will allow some vent this is not the primary aim of these gizmos). Extra insulation can be applied external to the TF studs but the render should not be applied directly to this. With render finish on timber frame there should be a vented and drained cavity behind the render system (and carrier board or mesh) but in front of the extra insulation. The performance of the insulation will not be affected in this instance. Sorry ProDave but I do not see any meaningfull approval, i.e. BBA or similar, on the link and your detail is not supported by TRADA (see Timber Frame Construction, 5th Ed), NHBC Standards or Building Regs. The fact that BC accepted it may simply mean a lack of undertsanding here. It is not a condensation issue but an issue with rain/moisture penetrating the render system and then having ready access to timber and wood based materials - the drained/vented cavity avoids this problem and is shown by the mainstream insulation manufacturers in TF systems. Ian

ProDave - is that an accepted detail? TRADA always show a ventilated cavity behind the render system - I believe this is to avoid moisture transmission through the render (& insulation) back into the timber frame.

Check product installation instructions and BBA certificates - due to this being a critical application ALL of the mainstream products, full and partial fill, will be certified. Walls will dry OK without a vented cavity. Due to fire regs the cavity must be sealed around openings and at the top of the cavity. Joe90 - was this a standard masonry cavity wall? type of insulation? I have never heard of cavity wall being vented in this instance. Sub floor vent should be ducted thru cavity. Should fire get into the cavity it is hidden and can spread, particularly dangerous is spread of smoke/fire into the roof space. Again check BBA cert for your cavity insulation. Full fill systems, in conjunction with render finish, can be used in severe exposure aeas if BBA certified.

Nothing to do with stale air or condensation - residual cavity is more linked to preventing driving rain penetration but also gives useful thermal performance, especially if insulation has a bright, foil face. Weep holes not classed as providing vent in this instance. Ian

The cavity in standard masonry cavity construction is not ventilated i.e. it is not provided with gaps/vents to deliberately vent the cavity. Benefit of low emisivity facings on cavity resistance and aircrete blocks externally can therefore be assumed. Correct in that any elements external to a ventiliated cavity are ignored (see BS EN ISO 6946 on U-value calcs). Insulation manufacturers tend to assume brick/dense block outer so contact them for alternative construction U-values. Ian