U-Value - Timberframe

Mike2006

Hi,

Just a (hopefully) quick question.

What is the real difference between 2 timberframe houses, one with a U-Value of 0.15 and the other with 0.2.

In monetary terms, what would you pay for the difference and in living with it terms, is one much better than the other?

Hopefully this question can be answered without having to have a huge understanding of u-values etc..

Thanks,

Mike.

Carlow52

<The calculation of u-values is measured as the amount of heat lost through 1 square metre of a material for every 1ºc of temperature difference between inside and outside.>

the the lower U value loses less heat so if u cost out the difference (0.2 less 0.15) in heat loss, grossed up by the area of ur house etc etc and do it over say 30 years, assuming certain cost rises in energy and then you discount the additional annual energy costs back at the current interest rate you get the capital cost of the difference in cost between the cheaper 0.2, versus the more expensive 0.15

The workmanship in either is critical

Mike2006

Thanks for the detailed response. However I was hoping to get a response from a different angle...


e.g. . Yes, there is a huge difference between 0.2 and 0.15. One is crap and one is really good.

or

There isn't really much of a difference in the overall scheme of things when you take the windows @1.2 and other factors into consideration..

...

Not sure if it makes much of a difference to the answer but I am installing a MHRV also.

Thanks again,

Mike.

Carlow52

the mhrv will require good airtightness.

on the difference between the 2 U values, what is the cost difference that u are being asked to pay?

Borzoi

Carlow52 wrote: »

the mhrv will require good airtightness.

on the difference between the 2 U values, what is the cost difference that u are being asked to pay?

Okay - sample calculation:
Say the house is 2 story, 225mtr floor total, and 2.5 mtr walls, and is square so 15 x 15 mtr. So you've 300m2 of external wall - of this say 80m2 is glass. So you've 220m2 of wall.

The heat loss form the house is Q=U.A.DT
On a very cold day Int Temp: 20C avg, ext temp -2C, so DT is 22

Wall_1 Q = .2 x 220 x 22 = 968W
Wall_2 Q = .15 x 220 x 22 = 726W
Not a huge difference - for probably a large capital cost to you

but lets look at you windows:
Standard double glazing Q = 2.8 x 80 x 22 = 4926W
Low E, Argon filled double glazing Q = 1.6 x 80 x 22 = 2640W

Big difference.

basically, for walls, IMO, 0.2 is good. Your money could probably be better spent elsewhere in the house improving the thermal efficiency

sydthebeat

Mike2006 wrote: »

Thanks for the detailed response. However I was hoping to get a response from a different angle...


e.g. . Yes, there is a huge difference between 0.2 and 0.15. One is crap and one is really good.

or

There isn't really much of a difference in the overall scheme of things when you take the windows @1.2 and other factors into consideration..

...

Not sure if it makes much of a difference to the answer but I am installing a MHRV also.

Thanks again,

Mike.

0.2 is a good value.

0.15 is a very very good value.

all things being equal, go for the 0.15...

Retro-Fit

Mike,

Make the calculations yourself in accordance with BR446 2006, which factors in timber bridging. The fact is that U-Values for steady state calculations at a point in a centre of a wall are often meaningless. Most heat loss for walls occurs at the junctions between materials. Windows, rising walls, eaves and services penetration through transmission and air leakage. So good design and detailing are critical. As Carlow says its all about the workmanship.

2 very important topics in Timber frame are thermal inertia, and moisture diffusion. when these are considered, the choice of materials in Timber frame panels become critical. Polymer derived insulants perform badly on both counts and natural materials excel.

Unfortunatly for most self builders, the consultants engaged in an architectural role are brough in just to 'git de plannin like', a house for life needs to be designed and supervised. We have a big problem in building houses for this century, we simply lack the skills to build properly. There are the small few who's buildings appear in Construct Ireland magazine but they are a tiny cohort.

http://www.bre.co.uk/filelibrary/rpts/uvalue/BR_443_(2006_Edition).pdf

Mike2006

Folks,

Thanks for all the responses.

I am out to a number of timberframe companies for tender at the moment.
As they are coming in I am reviewing them.

I had my mind set on a particular company for supply but then changed my mind after reading posts here on dispersion of gasses in insulation over time etc...

Company A can offer me 0.15 @ approx 100k. (rigid insulation)
Company B can offer me 0.2 @ approx €85k. (quilt insulation)

I have gone for a fairly high spec on the timberframe so thats why the prices are prob a bit higher than you usually see quoted here on other threads. (I have seen timberframe quotes of ~€30k posted here before)
Not all items are equal as the quote is not itemised in detail from company A so I can't remove the price for skirtings/doors/architraves etc.. I have reduced the price to reflect this though (as I will be providing those myself).

So, if it there is not a big deal between 0.15 and 0.2, then it is a no brainer.

Mike.

sas

Mike2006 wrote: »

Company A can offer me 0.15 @ approx 100k. (rigid insulation)
Company B can offer me 0.2 @ approx €85k. (quilt insulation)

I have gone for a fairly high spec on the timberframe so thats why the prices are prob a bit higher

Mike.

Those prices aren't a bit high. Unless the house is 5000 sq ft they are very high.

Define high spec? What depth of stud is being speced? What else are you getting for that price?

Mike2006

House is 3,600 sq ft.

Prices included VAT.

195 x 38mm stud.
Airtightness Membrane
High level of Insulation
Acoustic Insulation
Mid Floor to support 50mm easi-screed for UFH
Roof truss converted to allow for storage space in atic
300mm attic insulation
Felt & battens fitted
Digital Survey of slab prior to delivery of timberframe
Erecting of timberframe

No doors/skirting/architrave/stairs.

Only have 2 of 6 quotes back so far so there is still plenty of room for improvement on price...

Mike.

rodred

hi,

if its any use to you, i have received several quotes form companys
recently.
for 1350sq ft 2story with attic conversion c/w 2no. dormers on roof.
very well known company uses a tek sip system 80k ex vat inc internal doors etc.
other company in wexford, closed panel system came in at 54K ex vat
for uvalue of 1.8 on the walls, all argon filled low e glass, internal and external doors, windows, socket positions and intenal services conduit factory fitted. and additional 18k for factory fit external cementation board and apply acrilic render on site. if anyone could let me know if the price for the render board sounds about right, that woudl be great.

got another quote for builders finish passive levelish timber frame for 220k.
and another for passive level, frame only, no windows etc for 200k.

soldsold

Hi,

Would you mind PM me with details of the wexford supplier, that sounds like a great price.>>?

Thanks!

Steve

Bobbiblu

soldsold wrote: »

Hi,

Would you mind PM me with details of the wexford supplier, that sounds like a great price.>>?

Thanks!

Steve

+1 please

miss indecisive

Could i please get a pm of those details too

Thanks

rodred

pm's sent cheers