ADLIan

3 is very low so don't expect typical contractor to achieve this. Needs very careful design, great workmanship and meticulous attention to detail. The value is not known until tested on completion so if not achieved may need expensive remedial work. If measured the test result cannot be worse than 10. It is possible to avoid the air pressure test on a one-off house but a default air leakage of 15 must be used - probably resulting in a failure under Appr Doc L1A. Also 3 or less means you have to install whole house mech vent.

A&A in liquidation. Now morphed into Insulation South Wales with same owner. Draw your own conclusions. Not sure why anyone would use seconds in a floor (or elsewhere) especially in a self build, life time home. Variation in thickness may give voids in a floor system, made worse if used in multiple layers. What if the reason for being second quality is low compressive strength???? Worth noting also that if second quality product it will not be covered by BBA certificate or comply with Relevant BS.

As mentioned not much detail at moment. New build won't be covered as the scheme is for renovation and upgrading existing housing stock. I doubt DIY will be allowed either as works will probably have to be surveyed & approved by an 'accredited' inspector and then works undertaken by an 'accredited' installer/contractor. All works to PAS 2035 standard?

The SAP rating is based on energy cost. Using an ASHP means electricity is the main fuel. Whilst this is the expensive option it is offset to a degree by the efficiency of the ASHP. The SAP calculation is not very sensitive to elemental U-values so lower U-values will have little effect on the SAP rating. MVHR unless correctly designed (and installed) can actually increase energy use (uses more energy than it saves) and negatively impact SAP rating and Bldg Reg compliance.

The acoustic performance of intermediate floors and partition walls is arrived at by laboratory testing. If you chose not to follow the deemed to satisfy option in AD E then the manufacturer of the floor joist (in this case) should have a lab test & report (see App B of AD E) to prove their system complies with the Regs. The Hickman report does not appear to be to the correct BS. Hickman may have other test reports however in support of the above document.

All Approved Doc E covers detached houses - airborne sound (not impact) in intermediate floors and certain internal partition walls. The standards are not as onerous as those between flats or terraced properties. The AD gives details that are deemed to satisfy the requirements in detached dwellings but only gives suggested construction details for flats & terraced houses (in this latter instance actual compliance must be shown by pre-completion testing or signing up to Robust Details Part E scheme. Intermediate floors in dwellings normally incorporate 100mm of mineral wool quilt with min. density of 10 kg/m3 - note denser will necessarily be better! Some of the engineered joist manufacturers have products/details that omit the mineral wool but follow the MIs to the letter and ask for the test report to prove it.

It is not recommended or accepted good practice to render directly to timber frame or onto insulation on timber frame. Render should be onto a render carrier board with a vented and drained cavity.

The renovation/upgrade of existing floors, walls and roofs is covered by the thermal requirements in Approved Doc L1B (assuming England) which details U-values to be achieved. Building Control do have a degree of flexibility however and exceptions are listed. This type of work however is very badly policed by BCOs, perhaps partly because they're not informed. Lack of proof of Bldg Reg compliance here may affect any future sale of house.

There is normally a vapour control/separating membrane between the insulation and the screed which then inks to the VCL in the wall. If not done then above both seem to be reasonable solutions though a full membrane over the floor may be a bit of overkill.

Is '70' a typo error, should just be '7'? Problem with using the default value of 15 is that it probably results in a failure under Part L1A.

If windows enlarged the max area of new (& old) windows, door, rooflights should be no more than 25% of the floor area of the dwelling otherwise 'compensating measures' are required. See AD L1B. This could be as simple as convincing BCO that the 3G is better than existing windows or it could be full SAPs A lot will depends upon how clued up your BCO is and how fussy he is! Best to resolve this now.

Low e foil on pur is often certified by manufacturer, bba or similar. Reflective breather membrane, again certified, can make useful reduction in uvalue for clear cavity and brick outer but little benefit with render on carrier board

You should get U=0.13. Slightly better lambda for PUR and low emissivity air spaces next to foil faced PUR. Difference between brick outer leaf and render on board only impacts 3rd decimal place so still U=0.13. Your TF supplier may not be using 15% bridging in TF as required under Regs but I still only get U=0.12 at best. Get a U-value calculation from them and post it here for comment

MIs and BBA certificates for PUR cavity insulation show insulation on inner leaf. Mineral wool full fill can be built with either leaf leading. Leading with outer leaf is better practice.

Hi all. Just a few comments on this thread. The manufacturer is unlikely to overspec or ask for too many vents as the numbers can easily be checked. Possible loss of credibility & loss of sales. BR Appr Docs (& NHBC) require sub floor vent in both timber and concrete suspended floors. NHBC Standards are more prescriptive with the 2m max spacing. This is a good thing as fewer vents, further apart on one wall, is likely to result in pockets of still air between the vents. Could it be argued that the 450mm from each corner be measured from the internal faces of the wall. As above to avoid pockets of still air at this point if, for example, the nearest vents were 2m away.

Expensive option for such a small roof. Keep it simple and create the fall in the roof structure using firings

+1 to the above. Note the damaged foil will adversely affect the lambda value of the foam and will not give a low emisivity surface anymore. The foil does nothing for the fire performance, look at Grenfell.

Its often simpler and more accurate to get the manufacturers to run these figures for you - only takes a phone call or email. Looking at the calculation (I'm not familiar with the use of this software) I would comment; 1. Corrected/uncorrected - may be correcting the U-value for gaps around the insulation (as per the BS). Not required in this instance as you have 2 layers of insulation and the mineral wool is normally deemed to fully fill between the studs. 2. DP = dew point? Does not seem right in this position if it is.Especially with the inclusion of the AVCL 3. Architect is wrong. No need for an airspace. It will impact the U-value but making it higher! Leaving a 25mm airspace will give a low emissivity airspace with resistance 0.44 m2K/W. Filling this gap with 25mm of mineral wool gives a much higher resistance of 0.025/0.035=0.71 m2K/W Other comments; 1. The airspace between the plasterboard and AVCL is not low emissivity. It is high emissivity with resistance 0.18 m2K/W 2. You do not appear to have accounted for the thermal bridging of the studs in the140mm mineral wool and the battens in the service void

As I predicted. In floors you quickly get into case of diminishing returns with thicker/lower lambda insulation so U value will not improve much. Plus SAP relatively insensitive to changes in elemental U values

Requirement for pipe insulation is covered in Appr Doc L1A and the Domestic Building Services Compliance Guide

Go for pur. Only one manufacturer of phenolic so it’s priced accordingly! Difference in U-values will be small (especially in the floor) and should not impact SAP numbers to any degree. Get you SAP assessor to run the numbers. Second quality insulation is seconds for a reason; may not achieve the declared physical properties, may not comply with relevant British Standard, may not be fit for use under the Building Regs ......

It’s not the R value that should compared as this is thickness dependant - 300mm of woodfibre will have a better (higher) thermal resistance (R value) than 120mm of PUR! Comparator is the thermal conductivity (lambda value) as this is an inherent physical property of the material and is not thickness dependant. The U value refers to the total build up of a wall, floor or roof. The U value of insulation alone is meaningless. it must have been costly obtaining wood fibre with 3x the R value of PUR, approx twice the thickness and twice(?) the price

As above nothing to do with the thickness of the insulation, problem is the screed. Standard sand & cement screed onto insulation should be at least 65mm thick with light mesh reinforcement (or fibre reinforcement mixed in). The kitchen unit legs may have imposed too high a point load on the screed & insulation but this is unlikely.

+1 @ProDave From BS 5250 vapour resistance of 13mm OSB is approx 7 MNs/g. Compare to vapour resistance of 0.12mm (500g) polyethylene sheet at approx 250 MNs/g. This would be classed as a (A)VCL - the OSB offers little resistance.

The Standard uses -5 Deg C as external winter temp. Not sure what the other conditions are as I'm not directly involved in this sector. Normally the internal classes are low occupancy dwellings and high occupancy dwellings (there are others but not relevant here). A good PUR manufacturer with experience in flat roofing should have this info and work to this Standard. On the positive side I would imagine the construction would be relatively safe looking at the relative thermal performance of the PUR and mineral wool but proceed with caution! Was the calculation done by the manufacturer? I would expect a product name and reference not just ‘PIR’.