Sliding Sash windows (1.6 Uvalue) or Tilt and Turn (1.1 Uvalue)

Quack13

We have been looking at numerous different types of windows for the past month or so.

One of the companies we came across, a reputable company originally from the states (Mxxxxn) showed us their products and we were really impressed with them. They looked great and have heard great things about them from other people, even though they are on the more expensive end of things.
We particularly liked their alu-clad sliding sash windows.
According to the seller they have a U-value of 1.6.

Now here's the thing.
We intend on building a timber frame house with a high level of airtightness, and with external wall value of 0.16 - 0.20.

We have a dilemma here where we really like the window in question, however we are also spending a lot of money to insulate the house and make it as airtight as possible.
I would be interested in hearing people's opinions on whether a window with a Uvalue of 1.6 would just be a silly thing to install after spending so much time and emphasis on making the build as efficient as possible.

Is 1.6 THAT bad? Would a window with a value of say 1.1 or 0.8 make a massive difference?
If we spent extra care applying airtight tape around these windows etc, would that work. I do know that sliding sash windows are faulted in this respect by their very design.

Another quick note: I was talking to a salesperson from another company yesterday and he scoffed at this companies claims that they do a 1,6 window and said it was more like 2.1. It's hard to know with these guys as they are always knocking each other, name of the game i suppose. But is there any way I can independently verify the Uvalue that this company is claiming on their windows.

Q

sinnerboy

There is one UK provider of A rated sliding sash windows

http://www.bfrc.org/Consumer/search.aspx

Can't name them directly but click on
homeowner then
find your local supplier then
find windows

busman

Quack13 wrote: »

Another quick note: I was talking to a salesperson from another company yesterday and he scoffed at this companies claims that they do a 1,6 window and said it was more like 2.1. It's hard to know with these guys as they are always knocking each other, name of the game i suppose. But is there any way I can independently verify the Uvalue that this company is claiming on their windows.
Q

Disclaimer- I work in the fenestration industry!!!
I can safely say the whole u-value for windows and doors is a mine field
Many sales people haven't a clue about the difference
between Glass u-values (often referred to as the "centre pane" value) and Window u-values.

The most important thing to ask for is do they have any certification for their windows and who it is issued by?
i.e The BFRC. http://www.bfrc.org/Consumer/search.aspx
That will be a quick way to weed out the chancers! Ask for a copy.

Beware that without this certification, when your BER assessor inputs the values for your windows into the DEAP package he must use the default values given in Table 6a.

From this table the best double glazed u-value is going to be 1.7 for a double-glazed, argon filled (low-E, en =0.05, soft coat) window!!

Now if you take that the "centre pane" value for this glass on it own would be 1.2 you can see where people could get "confused"

A far as I know there is no "certified" u-values for doors, you must use the default values in table 6.

Hope that helps.

Carlow52

Is the BFRC regulated by Government or is it just self-regulation by a group of double glazed sales persons?

I am not suggestion that Gov reg is any better than self-reg but it is best to know upfront.

Quack13

Busman, thanks a lot for the link.

however, I am a little wary of buying windows from an independent UK seller, just in case anything goes wrong and the hassle involved.

I would personally prefer an Irish based company.

Thanks again.

busman

Carlow52 wrote: »

Is the BFRC regulated by Government or is it just self-regulation by a group of double glazed sales persons?

I am not suggestion that Gov reg is any better than self-reg but it is best to know upfront.

There is no government regulation for windows in Ireland. The only requirements are for the u-value for glass in Part L and for safety glass where required.

The BRFC are a body made up mostly of window systems manufactures. They basically just set the required standards for the size and type of window and how it is tested to get a u-value. These test are EN ISO Standards.
This means that all u-value can be compared like for like.

The BFRC does not test the windows, this is done by 4 approved "Independent Agencies"
More info is available here : http://www.bfrc.org/trade/getwindowsrated.aspx
A window manufacturer also has to get their manufacturing process certified by one of these agencies.

A certified window should have a little silver sticker on it somewhere with a certification number on it. This is issued by one of these 4 agencies to show that the window is manufactured under an "approved" process.
This label is in addition to the "rainbow" label that is usually put on the glass showing the energy rating and u-value etc. This label is issued by the BRFC.

The company I work for has 8 certification now for different window types and ratings.
To-date we have not once been asked for a certified energy rated window!!

busman

Quack13 wrote: »

Busman, thanks a lot for the link.

however, I am a little wary of buying windows from an independent UK seller, just in case anything goes wrong and the hassle involved.

I would personally prefer an Irish based company.

Thanks again.

There are Irish companies on the list for Casement and T/T windows.
Currently there are none for Vertical Sliding Windows.
It is very hard to get an A rated vertical slider window.
We are currently trying to get a B rating for our VS window but it will take some more work.
Our best Tilt/Turn is a "C" with a energy index of -12kWh/(m²·K) and a window u-value of 1.5W/(m²·K)

The BFRC have a pdf that give what the energy index of each band is ..
http://www.bfrc.org/pdf/ER27A%20Glassex%20leaflet%20final.pdf

Nick Elsulphide

When it comes to certification BFRC ratings are useful up to a point – a very limited point. The u-values are fine for DEAP as long as the assessor is happy with the fact that they only apply to the rated window (more anon).
SEI will not accept the BFRC solar factor as this applies to the whole window whereas DEAP specifically requires the solar factor for the glazing only. The figure for ‘effective air leakage’ is meaningless if you are worried about how your windows will perform on top of a hill in the arse end of Donegal. The industry standard test is at 50Pa (as are blower door tests) but the BFRC then divides this figure by 20 as the figure is “not suitable for use in energy calculations”.

A BFRC rating refers only to the “standard BFRC sample size – this is the same sample size used in both the relevant European Standards and in the Building Regulations. It is NOT possible to provide a BFRC Rating for any other specific style/shape or configuration of window”. In other words if the window is not 1230x1480 in size then it is not rated. Period. Thats not going to stop people claiming that all their windows are ‘A rated’ but in the absence of Trading Standards who’s going to stop them. This though is not the place for an in depth discussion on the BFRC scheme.

I would personally request performance (water/wind/air testing) certification from an EoTA approved organisation. BBA or IAB certs (or IFT-Rosenheim certificate if you want to risk eastern European product) would be a good example. Other things you might ask for would be evidence of CE marking & BS7950 security testing.

A couple of other issues raised in the thread;
Quack 13: 2.0 W/m²·K is CE declared by the manufacturer for their vertical sliders. Thats relatively poor as is their data for air permeability. This is right on the limit for TGD-L compliance but their pitch is lifestyle and not performance.

Busman: There are plenty of doors with certified u-values if you were to look a little
further beyond Bandon. The BBA online database is a good place to start searching and its a good way to weed out... ehh...chancers