What U-Value should I look for in windows?

SillyMonkey

Worked out roughly that the U-Value of my walls will be 0.21. So far have got 2 quotes for windows. The expensive ones have a U-Value of 1.1 and the cheap ones have "B rated" U-Value (need to clarify with him what excatly that is).

Just want to know if the 1.1 is overkill, I have no idea what the windows should be since there is no way it's going to be anyway near 0.21.

If 1.1 is not the required value, what would be to match the walls (if you know what I mean)

BTW i'm not going for any particular rating, just trying to do the very best I can for what money I have. Trying to get the best insulation in the house first any worry about everything else later.

ircoha

Have a read of the new regs at http://www.environ.ie/en/Publications/DevelopmentandHousing/BuildingStandards/FileDownLoad,16557,en.pdf see page 69 for summary.

This document also deals with the issue of the size of the glazed area.

I can guess who came up with the 'B rated' window, did they tell u who did the 'rating'.

What follows is just to give u a few pointers, it is not a definitive guide

If your wallet will take it, on the face of it the 1.1 is the way to go but the decision really cant be made in isolation: for example the extra x grand on the 1.1 over the lower rated window might be better spent on other aspects of the build: eg in insulating the roof better as the average house loses 25 to 30 % via the roof as opposed to 15% in the windows. or it might be better to buy a very efficient condensing CH system or a better insulated DHW tank or solar panels

Heat loss is a function of the temp differential so smaller windows in the living room ,which has a higher temp, may lose more heat than larger windows in the bedrooms, where temp is usually lower.


The is a document on passive housing on the page at this link
http://www.sei.ie/gsearch.asp?q=passive&sort=date%3AD%3AL%3Ad1&output=xml_no_dtd&oe=utf-8&ie=utf-8&client=default_frontend&proxystylesheet=default_frontend&site=default_collection

Have a read, you will get loads of ideas. I suspect you are not doing a passive house but the ideas are nevertheless applicable.
HTH:)

sinnerboy

1.1 for double glazed units is commonly avaliable . if you look for better than this the cost baloons

when a 1.1 unit is placed into a window frame , the overall window u value increases -the glass out performs the frame . so a 1.5 x 1.2 window may result in overall u value 1.4

you cant "match" the wall u value

ardara1

There are a LOT of bogus claims out there on the performance of windows - many UNITs use the Carey glass as their base which is a SOFT COAT low E glass having a U-value of 1.1 - but THEN you must account for the framing type. (Carey do not supply windows)

What ever supplier you do opt for - IF THE CAN NOT CONFIRM THE PERFORMANCE BY CERTIFICATION _ THE SEI WILL NOT ACCEPT THE RESULTS AS PART OF THE BER CALCULATION. So if you are using a very good CLAIM to use in the calculation - it may well knock the score back considerably when the BER is issued.

The A,B,C rating being quoted is used by the British Fenestration council in the UK - it's not based solely on the U-value of the window but also build/air tightness qualities - IT SI NOT ACCEPTED N IRELAND - yet! - hopefully at some stage it will.

The are good systems out there - and accredited by testing.

binnox

Hi,

Starting to build next monday and just paid the deposit on the windows. This was the biggest cost after the block work. I looked all around from Marvin to Munster and found that it really a balancing act

Price from Supplier
Service from Supplier
U values
Double or triple glazing

I ended up going with triple glazing with a glazing u value of .7. I only upgraded from double glazing because there was only a 10% price difference with the supplier I picked. I think that talking with suppliers and getting estimates and seeing the windows in place is time well spent. The windows will cost around 20K for 15 windows (all big - largest 3.35m * 2.1m), 2 Patio doors and front & utility door. All are wood and the windows are all alu clad.

For double 1.1 with the wood and alu clad I was getting quotes of 10K more.



Binnox

SillyMonkey

Thanks a million lads loads of good advice there.

Done some homework myself at the weekend trying to figure out what energy rating I am aiming for in the house. Surprisingly the architect didn't have a clue what energy rating he was after.

But looking at the way he has the house at default (as is on the plans) I need just a few adjustments to get an A3 rating. Like the walls for example I need to hardwall the inside walls. Just need to figure out by how much.

Binnox would you mind telling me who you went with in the end (or PM me I’m not sure what’s allowed). I'm probably not going with the crowd I got the 1.1 quote from. For A3 rating I need 1.3 windows but they only have white PVC at 1.3. I'm not going to waste my money on the 1.1s but the 1.1s are AlU clad which is what I want.


The SillyMonkey:D

250882

I had a window crowd in the office trying to sell me some alu clad windows a couple of weeks ago. They reckoned that triple glazing should only be used on the north elevation of buildings as triple glazing on the south will seriously reduce your solar gains.
I kinda agree, if you have a very well insulated house thats airtight then passive solar gain could be a very effective way of heating your space but i think that some form of insulated shutter over the windows is then needed for at night.

leon112

u-value 1.ow/m2k of glass.this standard has to be achieved by 2015 ,take this as a standard value for now, no need for triple glazing unles you want to bragg !

Slig

I agree, the insulation difference between triple and double glazing is tiny while the price difference is huge and you'll reduce you passive solar gains, better sound insulation from triple glazing though, so handy if you live near a busy road.

sinnerboy

SillyMonkey wrote: »

Thanks a million lads loads of good advice there.

Done some homework myself at the weekend trying to figure out what energy rating I am aiming for in the house. Surprisingly the architect didn't have a clue what energy rating he was after.

But looking at the way he has the house at default (as is on the plans) I need just a few adjustments to get an A3 rating. Like the walls for example I need to hardwall the inside walls. Just need to figure out by how much.

Binnox would you mind telling me who you went with in the end (or PM me I’m not sure what’s allowed). I'm probably not going with the crowd I got the 1.1 quote from. For A3 rating I need 1.3 windows but they only have white PVC at 1.3. I'm not going to waste my money on the 1.1s but the 1.1s are AlU clad which is what I want.


The SillyMonkey:D

Be carefull . "A" ratings are EXTREMELY hard to achieve .... . "B's" are tricky enough ...... Are you taking advise from a registered BER assesor ?

holdfast

having triple glazing will not hinder any solar gain. in fact a triple glazed window will provide more heat than it will lose in the year.[/I] Passive solar gain can provide 20% of you annual heating needs in a conventional house design to incorprate this. not a small amount in anyones terms. in a passive house this figure will rise as this is one of the primary heating methods

be careful anyone getting u values quoted they have to give the overall u value. this can make triple glazing not as expensive when comapring it to double. you should expect to pay 450-600 euro per meters quared for a good triple glazed window. there is a lot misinformation by suppliers and you really have to understand the information and about glazing before you can compare triple and double glazing from different suppliers. they may be little difference in a good double glazed (good overall u value and timber frame) and one where you are getting a triple glazed ( frame not insulated and large frame)?????? i was talking to one of these suppliers at the ernergy show his triple glazing were of a poor standard and would really have a u-value of 1.2.

blackiebest

OK, all here should stop confusing glass u-value with window u-value. The only way to tell the u-value of any window is to put it through a 'hot box' test. Otherwise it is an estimate. OP whatever windows you buy make sure the standard GLASS has a u-value of 1.1, i.e. argon filled soft coat lo-e glass. Depending on the scale of the window, the type of safety glazing used (toughened or laminated(use laminated)) the overall thickness of the glazing package etc will vary the u-value of the glass. 1.1 u-value is for 4mm glass - 16mm argon filled cavity - 4mm glass. This is what is used as the sales tool or claims by window/glass companies and accepted by assessors. Here is the kicker, depending on the frames, e.g. timber, PVC, Alum, Alu/wood and the profiles used, will vary the OVERALL u value of the unit. And to complicate it even more all the different species of timber have different u values, eg pine, meranti, larch, oak, sipo, eucalyptus, acoya etc...... I deal with this all day and really the whole u-value conversations are misleading. Buy quality windows, use timber frames or timber/alu, PVC is the devil to our planet, buy from a reputable company and concern yourself more with the quality of joinery, paint/laquer finishes and functions the windows offer. Make sure quality brand name hardware is used, concern yourself with the installation and integration details your chosen company offers and spend any extra funds you have on heavy quality curtains for your new home, 100% better than triple glazing when it is cold. The best windows in the world will always be the weakest point of a well constructed house and this is why you should judge this enormous spend after actually visiting many showrooms and finished jobs of the various companies out there. There are some very good companies selling very good windows and many s**te companies selling .....

Be careful and know what you are buying. They should be there a lifetime!

Good Luck.

SillyMonkey

Hello again. I am still looking at windows head is melted.

I have a BER assesor looking at the whole house. BTW I have decided to try and get an A3rated house at the end of this build. She said that it shouldn't be too difficult with what is already on the plans.

Anyway I got a phone call from her during the week asking me the dimensions of the windows for the house. After I told her I mentioned that I was looking at windows with a U-Value of 1.3 (including frame). She sounded suprised and asked why I was going for 1.3. I told her it was to achieve an A3 rating. She reckoned 1.7 would do, According to her calculator.

I have a meeting with her Mon to clarify everything but does this sound right to you?

sinnerboy

If she says so . No one element in isolation results in the rating .

sydthebeat

she should be able to show you what difference in kwh/yr windows of 1.7 and 1.3 make.....

make sure she goes over all the assumed inputs shes putting in as well... ie will all light fittings be low energy, or all bulbs?
has any assumption been made for airtightness?
etc

getfit

This link has the BER spreadsheet that is used to calculate the rating and a procedure book. I can get my head around 95% of whats needed, but things like heating appliances and kw/hrs is a bolve my head.... I've done my best to put in as much accuarte info as possible, but only one mistake and the whole calc is flawed, so I'm not taking the output as gospel.

It's still a very handy tool to get an idea of what's generally required though.

http://www.sei.ie/index.asp?locID=1543&docID=-1

Might be handy to have a BER spreadsheet sticky so people can help explain things to each other on the spreadsheet. What do the mods think????

I'm finding it a great cost/benefit analysis tool.... What will 3k on solar panels do to my rating compared with 3k on Windows???

sydthebeat

getfit.... its a hard tool to use without formal eductation on it....

the actual measuring conventions are somewhat different than you would expect... so if you dont know how to measure correctly everything down the line will be inaccurate.... to me thats the most important thing, get that right and your 50% of the way there....

regarding the more detailed inputs, if you are unsure of any input, use the default..... thats what any assessor would have to do...