Spec for a new build- thoughts

clarelady

HI
We are almost ready to submit our plans for PP and have an almost completed set of drawings and spec.
I would be interested to hear any opinions on the spec so far especially in relation to insulation and build choice.
House is approx 2900sqft and a 1.5 storey
I will try and load up plans when I figure out how to attach !

Ground floor construction
75 mm sand/cement screed on 60 mm K3 Kingspan thermafloor
Thermal insulation board on 150mm insitu concrete slab/raft on DPM incorporating a radon barrier on Radon barrier with sump on Sand blinded well consolidated hardcore
To give an overall U value of L24W/sqmK

External wall
100mm blockwork with nap render
100 clear cavity
100 blockwork inner leaf
60mm K8 Kingspan thermawall
Rigid board insulation
13mm plaster and render internal finish
To give an overall U value of 0.25w/sqmK

Cavity
Ties are to be of stainless steel and spaced at 450mm centers vertically and 750mm centers horizontally
Horizontal DPCs to be a min of 100m wide and 150mm above ground level DPCs at window and door openings to be dancor insulating DPC

DPCs
DPCs to all cavity walls to conform with BS 65? DR 743 and set 150mm above external ground floor level. DPCs also required at all heads, jambs and cills of all openings in cavity walls and to project 75mm into the back of all window and door frames
DPCs at window and door opening to be insulating DPC.

Cavity tray
Provide cavity tray DPC with stopped ends and lapped over vertical insulating DPCs and dressed into external leaf with weepholes at 1200mm centres
Internal walls to be 100 blockwork to be BS6073 with a min compressive strength of 3.2N m with light weight plaster finish

FF finish
75mm sand/cement screed on 150mm holocore precast concreate floor units all sized and fitted in accordance with structural engineers details with plasterboard on battens with skim finish to ceiling below

Lateral Restraint
Hollowcore units to be tied to external wall with 30X5mmX1200 long restraining straps at 1000 centres

Pitched roof construction:
Softwood C16 Grade rafters 50X150 at 400mm centres to receive roofing felt overlapping at ridge provide 36X22mm battens to take roof slates black 200X75 purlin fixed MD span and braced to 75 X 50 sole plate.
Provide and fix 50 X200C16 grade ceiling joist at 450 centres with 190mm K7 Kingspan insulation board laid between joists to give u value of 1.20w/sqmK
200X50 ceiling joists with 125mm plasterboard and skim finish to take 1 undercoat and 2 finish of emulsion
All fixed on 100X75mm wallplate strapped to blockword at 1800mm centres with 900mm long galvanised steel straps

Fascia and soffit
Shall be in good quality pre treated softwood fixed with rust proofed fixings countersunk below the surfac of the board and holes filled. Provide 25mm continuous vent gap at eaves fitted with anti-infestation mesh. Provide and fit CATNC roof space ventilator at each rafter.

External windows DoorsAll external windows and doors to be hardwood stained double glazed with Low E glass and fitted with proprietary trickle ventilators to provide background ventilation

Background ventilation
A min of 6500sqmm to be provided to all habitable rooms by window or wall vent

Studwalls
100X50 SW Studs with 450mm C/C cross ??? with 100mm rockwool insulation and finished with 12.5 plasterboard and skim to take paint finish

LoTwan

The uvalue requirements at present (& I'm happy to be corrected) are .25 in a floor without UFH & .27 in a wall. I know the wall value is set to drop early this year to .21.

I, personally, would increase the insulation in the floor & the walls.

Have you had a prelim BER done on the drawings? Where did you come up with the specs you have? What BER rating are you aiming for?

clarelady

we are going to have UFH downstairs , so its 0.24 with UFH and the wall U value should read 0.25 not 1.25 , do you still think we need to increase insulation ?This spec list is from the draft drawings we have got done up by a ATNo BER has been performed on these drawingsWe would like a fairly high BER ie A3 if possible

mickdw

I dont see you getting near the regs with those insulation levels. From what I see, you need to far exceed the minimum standards for each element to even meet the current regs never mind get an A rating

bruschi

clarelady wrote: »

we are going to have UFH downstairs , so its 0.24 with UFH and the wall U value should read 0.25 not 1.25 , do you still think we need to increase insulation ?This spec list is from the draft drawings we have got done up by a ATNo BER has been performed on these drawingsWe would like a fairly high BER ie A3 if possible

just on the build, you have in for hollowcore slab on first floor, so would you not do UFH on that as well? and instead of studwork, do the walls in blockwork?

DOCARCH

clarelady wrote: »

we are going to have UFH downstairs , so its 0.24 with UFH

U-value of floor for UFH should be 0.15 W/m2K. This usually involves providing 120mm of insulation to the floor.

Who is doing the spec for you? To be honest, for a new build it's a little basic. I would at least suggest a 120mm cavity with 80mm insulation. I would also look at insulation spec for the roof - far better to have insulation between joists and under (or over) joists to limit/reduce cold bridging.

LoTwan

DOCARCH wrote: »

This is not correct. U-value requirement for UFH is 0.15.

Who is doing the spec for you?

You beat me to it

If your planning application hasn't gone in yet you will need to meet .21 in the walls, not .27.

As was said above you won't get an A rating with the specs you have above.

sydthebeat

did kingspan spec your house???

using the K range is the most expensive board type insulation... it is a phenolic material whereas the other choices are polyurethane and polyisocyranuate... both these other types are cheaper.

using board insulation in walls is fast becoming an antiquated way of building. Its a common acceptance in the building industry that the u values calculated for board insulation are the absolute best theoretical values possible... whereas the actual long term performance values will certainly be worse. U values do not include for ill-fitting boards, warpped boards, mortar snots keeping boards apart, thermal looping etc... theres so much that can affect the performance of board insulation i would be confident of saying that there has never been a dwelling built like this that achieved the theoretical u values.


as far as the spec goes, id argue its very borderline as to whether it actually meets current building regulations, never mind the update regs which you will probably have to build to.

also, your specification for your heating system is just as important.... you need to know what renewables you are incorporating, what primary and secondary heating systems.. and how you are going to control these. These are all covered by regulations too.

clarelady

Thanks for all the replies and advice, now im a bit scared as havent a clue about this stuff. will take on board what you all said and def need to increase the insulation a good bit.
We def want to get a well insulated and low cost of running house. An eng did up our plans so maybe that is why the spec is low.

We want UFH downstairs only as we want to have carpets upstairs so rads would be better. also OFCH for heating purposes with solar panels for water. Not considered the HRV yet.IS there someone we can give our plans to to evaluate the level of build we would need to meet build regs as well as get to a A3 standard BER ?

stupid q but the spec you put on the plans for PP , do you have to stick to that when building , and is that taken into account when deciding the decision ? thanks for all the replies and advice it is all very much welcome and needed

2sounds

+ 1 all above. Remember at this stage to consider building orientation for maximum solar gain , although you may not have a choice here. Not seen reference to airtightness either which is also now part of regulation. Your uvalues / insulation need to improve.