Improving performance of newbuild house

[ryfly]

Hi, longtime lurker and first time poster. I've recently moved into a new build house and would like to improve its performance with minimal disruption (insulation, airtightness and anything else anyone can suggest).

 

Unfortunately I purchased the house at too late a stage in construction to have any real say on the build specification/quality.

 

It's ~150 square metres, timber frame house with block external walls and an integrated garage. Ventilation is provided via a PIV system in the loft (no electrical heater) and heating is from mains gas with standard sized radiators. Hot water is from a 170l unvented indirect cylinder.

 

According to the builder the house is built as follows from outside to in:

Render, concrete blocks, 50mm cavity, timber frame and insulation, vapour barrier, 50mm service void, plasterboard.

 

The EPC gives the following information (score 83):
Airtightness: 5.3m³/m2/h (as tested)
Roof U value: 0.15 W/m2/k
Wall U value: 0.28 W/m2/k
Floor U value: 0.23  W/m2/k (interestingly this is about 0.05 higher than houses on the same development which don't have an integrated garage - I'm unsure of the reason why).

 

My thoughts on easy wins:

- To significantly improve airtightness I believe I'd need to remove plasterboard covering the service void (expensive and a lot of work); can I do much without doing this; I don't want to tear a new house to pieces so trying to do as much as possible "non invasively", likewise don't want a plasterboard tent!
- Seal ceiling roses and cable entries into sockets and light switches with Orcon F airtight sealant.
- Seal cable and pipe penetrations on inside and outside of wall (outside block and inside internal plasterboard) with above sealant.
- Seal any larger gaps (potentially around extractor fan pipework) with blue airtight expanding foam/airtight sealant as appropriate.
- Fit (and seal) airtight down lighter hoods to upstairs bathroom and ensuite downlights.
- Add 170mm additional loft insulation (Reduce roof U value to 0.095 if my calculations are correct).
- Insulate exposed hot (heating and dhw) pipework. Increase cylinder pipe insulation from 9mm to 13mm thickness PE foam (19mm is over 3x the price of 13mm)
- Thermal camera review and basic pressure test using hob/wet room extractor fan.

 

I noticed during construction that the internal plasterboard only came to about 2 inches off the floor and the rest is sealed by skirting. Is this normal / should I do something about this?

Is there any benefit to insulating cold water pipes? I know passivehaus says yes, but what's the benefit in a normal house?

 

Thanks for your input.

[Moonshine]

How about this course of action, get an air tester back to your house, suck the air out of the house and he and you will be able to feel where the air leakage paths are, and they will be able to help advise on remedial works.

 

In a timber frame house i would have expected a lot better performance, but they will look at the comment fault areas.

 

This may cost you £200-300 but it may save you a lot of work in areas its not needed.

[SteamyTea]

Welcome

 

As above, get it re air tested and see how accurate the initial number really is.

You can make your own 'fan that fits in a window/door' cheap enough to trace leaks.

 

If you can borrow a thermal imaging camera, do so.  Then overheat the house and get outside on a cold night and take lots of images.  That will show heat loss paths.

You can take lots of the inside as well as I suspect many will correlate.

Only problem with lots of IR picture is remembering the order and place they where taken.

 

Shame it only has PIV and MVHR, just pushing warm air out the building.

 

Get some energy monitoring going, hourly data is so useful.

[AliG]

What kind of actual heating costs are you seeing?

 

Those are pretty poor insulation values. The house has been specified to the absolute bare minimum to pass building regs and as built performance is probably worse.

 

The highest bang for your buck will probably be in finding any wall penetrations and sealing them. It seems you have already identified this. Also I would see if you can seal the bottom edge of the skirting or take it off and seal the bottom of the plasterboard. This is a massive air path compared to sockets etc.

 

As you say, adding loft insulation is the cheapest way to improve insulation levels.

 

On top of an airtightness test, I would consider borrowing/renting an IR camera which will show up any problem areas.

[ProDave]

How thick is the timber frame?  That wall insulation is pretty poor, I am surprised it even met building regs?  Where abouts are you so we know which regs it should have complied with?

 

Make yourself a DIY blower door, using an old office fan or car radiator fan.  It will let you find where all the air is leaking in and out.  Most of the leaks will be lack of detail, there is no mention of an air tight layer so assume there is not one.  

 

If you really want to improve it it would be very intrusive, get back to the bare frame, overlay more insulation inside the frame, proper air tight layer, service void, then plasterboard.  Something that is oh so simple and not very expensive when building, which is why it annoys me so much that the mass market builders don't do it.

 

I bet your service void is already a plasterboard tent not least with cable penetrations up into the loft.  When you next get a windy day, unscrew one of the switches or sockets and I bet you are greeted with a blast of icy cold air coming out of the socket hole.

 

 

[ryfly]

Thanks everyone for the overwhelming response so far! I'll try to answer all the questions, apologies if I've missed anything!

 

I can borrow a thermal camera from work so that's high up my list.

 

How would I go about setting up energy monitoring? Not currently in the house so can't comment on heating costs just yet, but want to reduce them as much as practicable.

 

Feeling the pain that if I got in a few months sooner I could've expected (and paid for) a much higher performing building, rather than fighting for marginal gains now.

 

I'm not sure of frame thickness, I guess I can estimate next time I'm at the house by measuring the total thickness of the walls from inside to out.

 

I'm in Northern Ireland, and unfortunately the building regulations were only updated in June 2022 for the first time since 2012! Since planning permission was granted before June 22 the only requirement is to meet technical booklet F1(2012) standards. Average limiting u values in this document are wall 0.3, floor 0.25, roof 0.2 - so very slightly above the standard. (This was lowered in 2022 to 0.18, 0.18 and 0.16 respectively).

 

How much can I feasibly do to minimise "plasterboard tent"...I assume there's no real way to do it other than to identify leakage paths with leak tester/IR camera, cut out/drill a hole in plaster to access the service cavity and try to plug hole in insulation either with airtight expanding foam or other means? Ideally I'd like to not "destroy" the brand new house in the process of fixing the issues.

 

I'll have a look at sealing the bottom of the plasterboard, I assume this won't cause any unexpected issues?

 

How would you expect an independent blower test to compare to a builder commissioned one?(I dread to ask, presumably significantly worse?)

 

Have I missed any likely leakage paths potential major issues that anyone can think of?

[jack]

What can you access if you take the front off each power socket? Might be some easy wins there that won't require any redecorating.

[Redbeard]

Limiting U values are not targets, though, so as others have said the values achieved look pretty disappointing. The way of calculating compliance with B Regs for new-build is based on a sort of 'pick and mix' insofar as you could get away with higher-than-ideal air leakage if you had better fabric U values and vice versa. The limiting u values are simply 'it cannot be higher (worse) than this'.

 

Is there a membrane behind the plasterboard?

 

What's the insulation? If foil-faced is it taped?

[Mr Punter]

I can't work out how you got such a good score (83) with such poor insulation.  Do you have solar panels?

[Andehh]

Don't forget the context before you fall out of love for your house.

 

Buildhub is here for the extreme high end of the market, so your scores are not great to this forums standards, but that's still a better score then 90% of homes on the market, and all the savings you mentioned might save you £15-20 month.  Top up loft insulation, and some additional detailing around the edges will get you an extra a few% few average UK home.

 

I imagine your heating bills anyway won't be much more then £150 a month?

 

 

[Iceverge]

what stage is the house at?

 

Any pics and it might give an idea of what can be done. 

 

 

[ryfly]

On 18/01/2024 at 14:31, jack said:

What can you access if you take the front off each power socket?

 

Not a lot unfortunately, just the metal back boxes and their respective cable entries

 

On 18/01/2024 at 14:40, Redbeard said:

 

Is there a membrane behind the plasterboard?

 

What's the insulation? If foil-faced is it taped?

 

There's a foil layer behind the plasterboard, it looks similar to what's on the outside of the timber frame in the cavity between timber frame and block (Fast house protec thermo tf200).

 

I'm not sure what the insulation is, I've never seen the buildup of the actual walls. Do you have any suggestions for how to find out?

As best I can tell from outside-In. Render, block, cavity, protec thermo tf200, main timber frame with insulation, another foil layer (maybe the same thermo tf200 maybe something else), service void, plasterboard.

 

On 18/01/2024 at 15:47, Mr Punter said:

I can't work out how you got such a good score (83) with such poor insulation.  Do you have solar panels?

 

No solar panels, I would guess that houses in NI will score better than mainland due to less stringent insulation requirements, although I may be wrong. They were updated about a year ago to be more inline with mainland UK but takes a while for new houses to be built to latest specs - anything with planning permission before release of the newer specs is given grace.

 

On 22/01/2024 at 06:21, Andehh said:

Don't forget the context before you fall out of love for your house.

 

I imagine your heating bills anyway won't be much more then £150 a month?

 

Absolutely, it's just something I'm interested in so want to make small improvements wherever I can. I'm not in the house yet but would hope that you're right!

 

On 29/01/2024 at 14:18, Iceverge said:

what stage is the house at?

 

Any pics and it might give an idea of what can be done. 

 

It's fully built and completed. I can't upload many pics here due to the size limit, but I've added an external pic of the in progress build and a few internal ones here - obviously I don't have anywhere near this level of access still! https://drive.google.com/drive/folders/1BnYxMUQApHUmg8jBVfSBg8B8tSaM_n43

Edited January 31 by ryfly

[MikeGrahamT21]

What has triggered your want to improve the house? Are you noticing any effects from poor workmanship? Or is it simply because the numbers look poor?

 

Also worth looking into https://www.aerobarrieruk.co.uk/