u- values confusion

nlbyrne

Hi,
We are planning our self build for this year and the budget is TIGHT (isn't it everywhere!)

We are currently pricing up TF companies to provide a pre-insulated frame.
What I am confused by is what U-value gives a warm house.

I know there are alot of variables but what is the most commonly "aspired to" U-Value of an external wall.

I know smaller is better but would there be a huge difference between 0.15 and 0.18 or would the difference be unnoticeable?
Thanks

sydthebeat

nlbyrne wrote: »

Hi,
We are planning our self build for this year and the budget is TIGHT (isn't it everywhere!)

We are currently pricing up TF companies to provide a pre-insulated frame.
What I am confused by is what U-value gives a warm house.

I know there are alot of variables but what is the most commonly "aspired to" U-Value of an external wall.

I know smaller is better but would there be a huge difference between 0.15 and 0.18 or would the difference be unnoticeable?
Thanks

Current minimum regulation up values will lead to 'warm house'. You need to have a preliminary BER assessment done on your plans to find out what minimums you must at least start at. A good assessor can do a ' bang for buck' analysis on the increases of insulation levels.

Todays regulations are very good. They lead to a very efficient house once the workmanship matches the goals.

There is of course a critical mass of insulation where the law of diminishing returns kicks in.

Its all about balancing the build budget with your expected running costs... You can front load the costs of running into the build by exceeding minimum regs.

heavydawson

nlbyrne wrote: »

Hi,
We are planning our self build for this year and the budget is TIGHT (isn't it everywhere!)

We are currently pricing up TF companies to provide a pre-insulated frame.
What I am confused by is what U-value gives a warm house.

I know there are alot of variables but what is the most commonly "aspired to" U-Value of an external wall.

I know smaller is better but would there be a huge difference between 0.15 and 0.18 or would the difference be unnoticeable?
Thanks

I'd make the house smaller before I skimped on insulation and air-tightness. What you don't invest in now, you'll pay in bills over the lifetime of the house in heating. Insulation is a relatively fixed cost now, whereas heating over the next 50 years isn't.
Really work through your plans to reduce the volume your heating, pack in as much insulation as you can, and spread the finishing costs over the next few years. And look at air-tightness in a serious way. When you're insulating to any reasonable level, draughts become a major heat loss factor.

nlbyrne

Thanks for the reply.

We already have planning permission for a 2400sqft bungalow. It's too late to go back to planning for us.

We are obviously going to get as much insulation as we can afford, and air tightness is on the "LIST" but if we ask anybody in the industry they are trying to "sell" something, where if we knew what an acceptable level is or the aspired level of u-value is we would know where we would like to be, Sorry it's hard for me to explain.
obviously the current building regs are the minimum but we would be hoping to go a good bit beyond them, but what is the "ultimate U-value" that people are happy with.

heavydawson

nlbyrne wrote: »

Thanks for the reply.

We already have planning permission for a 2400sqft bungalow. It's too late to go back to planning for us.

We are obviously going to get as much insulation as we can afford, and air tightness is on the "LIST" but if we ask anybody in the industry they are trying to "sell" something, where if we knew what an acceptable level is or the aspired level of u-value is we would know where we would like to be, Sorry it's hard for me to explain.
obviously the current building regs are the minimum but we would be hoping to go a good bit beyond them, but what is the "ultimate U-value" that people are happy with.

The u-value is used more for marketing these days than a practical measurement. When it comes to things like windows, there's separate u-values for the pane, and the frame+pane combined.

As an example, I'm in the middle of a self-build right now, and we're going for 0.12 in the walls, floors and attic. The windows are not the most energy efficient, but the missus wants sliding sash, so we're looking the best efficiency we can get there of 1.1

I'm spending what will probably amount to 1/10 of the total build cost on insulation, and I plan to get my air-tightness down to < 1 ach / hr after that.

Ultimately, you could I suppose go on the ballpark 10% figure of total cost, and work out what you can get for that. A quantity surveyor would be a very good idea for you at this point.

sydthebeat

nlbyrne wrote: »

.............., where if we knew what an acceptable level is or the aspired level of u-value is we would know where we would like to be, ................

sounds like you have NO professional input into the compiling of your construction specification.

Thats a huge mistake. Right now your just throwing darts in the dark.

Your starting point is a preliminary BER assessment. After you go through this step the light will be turned on.

heavydawson

sydthebeat wrote: »

sounds like you have NO professional input into the compiling of your construction specification.

Thats a huge mistake. Right now your just throwing darts in the dark.

Your starting point is a preliminary BER assessment. After you go through this step the light will be turned on.

Have to agree with Syd. BER should come first, and a QS afterwards to possibly help you explore the cost of insulation options to actually meet the BER.

fclauson

nlbyrne wrote: »

...
We already have planning permission for a 2400sqft bungalow. It's too late to go back to planning for us.

Getting new planning permission will be cheap compared to a cold house

also if you resubmitt with a smaller - more energy efficient house then you can only win because I think (and correct me if I am wrong) that they cannot recind the old permission and not grant you the new one - the new one can have a clause saying it replaces the old mind

gooner99

fclauson wrote: »

Getting new planning permission will be cheap compared to a cold house

also if you resubmitt with a smaller - more energy efficient house then you can only win because I think (and correct me if I am wrong) that they cannot recind the old permission and not grant you the new one - the new one can have a clause saying it replaces the old mind

I believe this is correct,we went for change of house (reduced from 240sqm to 140sqm) and extension of duration (extra 5 years) at the same time.As far as I'm aware we can build either house. There was a snag with my change of house planning, whereby we also changed orientation and they granted with a clause that we change the orientation back. I think we would have needed to ask for "change of house type and re-orientation" and not just change of house type. Not great as we designed the new house with passive gains in mind. So I'm exploring the options as to whether we can ask for change of orientation or need to go for a full new planning to achieve this. So we could possibly end up with 3 choices when all is said and done.

fclauson

my view would be replan in if you can - paper, time and processs is cheap - blocks,cement and a life time are not

nlbyrne

Thanks Guys,

can I ask, how long did the "change of house type" take to go trough the planning process? I have the original plans I drew up already downsized by 20% with the exterior and interior layout etc all looking the same but with it shrunk.

This might be an option if it's not going to take us forever