Advice on build specs and BER after planning granted

bifl

Hi,
Long time reader on this forum and sub-forums , I have learned plenty on here (coming from a low base !!) and been given plenty to think about that will hopefully help me achieve a successful build. One thing I do take from all of this is that there is not one agreed approach out there if you want to achieve particular spec or whatever and a lot comes down to the quality of install and workmanship.

Now am at the stage where I have planning permission for a 2650sq ft house and now what to move forward and hope to begin building in the new few months through a tender process. From talking to the Engineering the next stage is for him to turn the drawing into tech drawings which will then be given to a BER person to determine a provisional BER and DEAP calculation against the Building regs Part L and against my expectations which is for a high level of insulation and airtightness and a BER of A2/3 if finances allow. This combined input will then go to tender.

What I know is going into the build is as follows. The engineering is talking about a 250mm fully filled beaded cavity and triple glazing throughout. For me then I would like ground source geothermal UFH and a MHR system. Other spec is 1.5 air changes an hour as a means of ensuring that the tender/builder has to meet a certain targets and thus a certain quality of build as a consequence. As I’m going geo from what I have read here on boards it’s best to fill the cavity and do not have any insulation on the inner walls so they can act like a thermal store. So from this is where my question now a rise.

On the BER side what service would I want from them?
I was thinking of the following
- provisional and final BER
- DEAP calc for Part L compliance which will then drive certain elements within my build which go back into the technical specification/drawings
- 2 air tightness tests to ensure build is progressing correctly and then that final specifications have been met as regards 1.5 air changes an hour.

To achieve my expectation
- what depth, type or u value of floor insulation would I want?
- I need to get a good BER person, what would such a service cost from a BER person cost roughly (inc vat)?

Any other comments on any of this would be appreciated to challenge my approach, spec or anything else !!

4Sticks

You have a pretty good overview grasp there.

- be thinking of 200mm EPS insulation / U Value 0.1 w/m2K for the floor
- budget €400/600 + VAT for a good BER person to input all info into DEAP and then be on call to meet or over phone e-mail say 3 / 4 times to runs various what if scenarios ( always remaining in Part L compliance of course ) to help tie down the spec.

MicktheMan

To add to 4sticks, ensure your ber person can advise you on thermal bridging and its consequences if not designed out of the build.

Given your build target wrt insulation, airtightness, ventilation and ber rating, have you considered a passive build?

blast06

Small point....
250mm is a massive cavity obviously. If you went with say a 200mm cavity and Quinn lite blocks on inner leaf (achieving more or less same u-value as 250mm cavity .... possibly slightly less but all but negligible) then if you have say 70m of external walls (i also have 2650 sq ft and ~73m external walls) then you add ~3 sq m additional floor space to your finished product. Indeed to achieve an A2/A3 i think a 150mm cavity with quinn lites on inner leaf should get you there and that would give you an additional 6-7 sq m of additional floor space.
Cost difference from my non-QS direct-labour experience ..... quinn lites on inner leaf ~€1000 extra for blocks but ~€600-700 saving on amount of bead you have to get pumped if you scale back to 200mm cavity (probably €100 more for screed too).

Couple of other tips from my experiences.
- Even if you don't go with Quinn lites then putting them down as the first line of blocks on all internal walls will help reduce thermal bridging.
- Put a sheet of polythene on top of floor insulation before pouring screed .... reduces degradation of floor insulation over time (i'm sure others can give a more technical explanation!)
- I would be surprised if triple glazing would be required to get A2. Yes, for sure it will result in smaller heating bills but try and determine how many years it would take to pay back the additional cost of going triple glazing (i decided against it plus i reckoned i'd really appreciate the extra couple of grand at the end of the project !!)