ADLIan

Denser mineral wool rolls and slabs normally have a well defined thickness (not like the fluffy loft insulation). Try manufacturers websites for best products and best install method.

Ridiculous situation of local authority introducing these conditions and not having a clue what they are doing. Sometimes there is a get out clause stating if the planning condition makes the scheme not economically viable the condition can be dropped. A scheme of 17 houses near me had a similar condition dropped when the developer made a simple statement to this effect but no figures or costings to back up this statement! Has the local authority a 'sustainability officer' or similar you could ask.

I come across these types of planning conditions on a regular basis and it is obvious that they are written by people who don't know what they are talking about. You actually have 2 slightly different conditions here, I normally deal with these as follows; The 19% reduction in DER over the TER is simple and will probably mean using renewables/low energy (need to check with the planners what is included or allowable here!) The 28% reduction is arrived at by removing all of the above renewables and comparing the DER/TER (this dwelling may fail the Regs but this is not an issue for the planning condition). Ask the question of the planners - doubt you'll get a sensible reply! As above get an OCDEA on board asap to advise.

In the calculation above layer 4, TF200, needs setting to zero. The 0.77 value for this is only valid when against an unventilated airspace. This increases U-value to 0.26.

As mentioned above most BCOs probably wouldn't recognize a thermal bridge if it fell on them. Advise you to get a SAP assessor involved asap. Part of the assessment is to look at all of the linear thermal bridges (around windows, junctions of elements etc). Do not let the assessor use the overall default y-value for the effect of thermal bridges! You cannot estimate the effect by calculating the U-value at this point - 2 dimensional thermal modelling is used to assess the junction.

XPS will cause plasticiser migration in cables same as EPS - keep them apart!

An ASHP may not help - may actually make the SAP score worse!! It means your space/water heating are all electric which is about the most costly fuel (though offset to a degree by the efficiency of the ASHP).

The SAP score is based on fuel cost, as such elemental U-values do not have a great impact. The choice of space/water heating system and fuel will have a much bigger impact. Solar PV can help too. Get the SAP assessment done and see how the numbers stack up - a good assessor will advise on cost effective solutions.

Insulation manufacturers are normally exact with their U-values. Looking at the above calcs; the service void airspace is unlikely to be low emissivity (only if AVCL is reflective/foil) anything external to a vent airspace is ignored and external surface resistance set to same as internal See BR443 on U-value conventions and BS EN ISO 6946

The BBA certificate referenced above is no longer valid. Looks to have been withdrawn in Feb 2016.

They’re effectively the same product . Other manufacturers also available

In a pitched roof construction insulation between/under rafters = cold roof construction but warm roof space. If all/majority of insulation above the rafter this is a warm roof construction (& warm roof space)

You need to check with Tyvek and their instructions & BBA certificate. This will show required gap any ventilation requirement. Compliance with a bba is deemed to comply with the Regs

MI = manufacturer instruction. Check certification very carefully for use in severe exposure zone and compliance with Regs

Don’t think expanded glass beads are certified or have a history of use in this application.

Slates are quite well sealed and I believe even with a breather type membrane the roof void should be ventilated unless the membrane is certified (BBA or similar) to allow use unvented. construction moisture drying could be part of the problem.

West coast of Ireland + severe exposure + full fill insulation = probably not a good idea. Check MIs, Certification and additional requirements for protection of the wall from wind driven rain (render, tile hanging, rainscreen).

This late in the process solar pv will be the simple, cost effective solution.

The above link references a BBA cert that appears to be no longer valid. The replacement certificate now includes the vent cavity behind the cladding system. Check MIs and 3rd party certificates for exact requirement, accepted good practice is that render should not be applied direct to TF or insulation on TF.

How is eaves to ridge vent provided in that construction?

SAP always includes a heating system, if none specified then default is electric so no need to hide any dedicated outlets.

Approved Docs do cover heat loss from pipes and reference the Domestic Building Services Compliance Guide.

External wall becoming internal? No vertical dpc?

With plasterboard on dab you can add the thermal resistance of the airspace (& dabs) too so will be better than wet plaster. Where wet plaster may offer an advantage is in improving the air tightness of the wall.

Second quality insulation would not be fit for use under the Regs. as it will not comply with the relevant BS, carry CE mark or be BBA approved. Not sure how well this is policed though. Also insulation may be branded as a second for not being the right thickness but more seriously may also have failed other tests such as compressive strength or thermal performance.