Coming at it from a slightly different perspective, I have been trying to find out who makes the most weather resistant windows. I live in Shetland and wind driven rain is a major issue. NorDan are much in favour with local architects as experience shows that they keep the water out. The British and DIN standards specify that the windows should withstand wind driven rain at at least 600 Pascals pressure (if I have understood it correctly). NorDan claim to withstand 3200 Pa and Adpol 2000 Pa. I have just spoken to somebody from the Rawington HQ in Germany (?) who said that they only test to the standard, i.e. 600 Pa so I have crossed them off my list. I am waiting for a reply from Internorm.

Hello Maren,
I've just got my quote from Broxwood, and they look like they'll be around 1500-2000 (20%) cheaper than Internorm by the time the door quote comes through (they're pricing windows and doors separately)Lead time is 10-12 weeks though.

That's a good point aa44,I must check up on that too...

Thanks fostertom and MarkBennet: Is external insulation still a reasonable option if I only have space on two sides of the house? Third side next to an already extremely narrow driveway with no space left to sacrifice, fourth side will be the extension.

My parents in Germany had external insulation (EPS plus render) put on their house and the effect was impressive, noticeable even before the heating bills came in. I was told though that external insulation (which I favoured thanks to my parents very positive experience) would prevent the cavity walls from breathing - how would you account for that?

Thanks valasay, for the update, have sent an enquiry to Broxwood today but with those lead times I may not be able to order from them. Although I did read in Rawington's brochure that alu-clad windows should only be put in after absolutely every other messy job was done as render or plaster may damage the windows. Have you been told anything about that?

Posted By: MarenThird side next to an already extremely narrow driveway with no space left to sacrifice

OK, that's where 'without seeing it' comes in - think of something else maybe internal for the Grd. Fl, return to EWI for 1st. Fl, tho it's a double pity to suddenly bring the insulation line inboard - creates lossy thermal bridging situation. Consider extremely insulative (therefore only one third as thick) but expensive Aerogel for that wall. Obviously not he fourth wall you're building against, except above its roof line, if lower?

Posted By: MarenI was told ... external insulation would prevent the cavity walls from breathing

Rubbish - EPS is adequately breathable, Pavaclad very breathable. Closed-cell XPS (extruded polystyrene) and the other foamed plastics are not breathable and cost more. You'd need to use XPS below GL, down to top of strip found.

p38 of http://www.natural-building.co.uk/PDF/Pavatex/Pavatex%20Walls/090128_Technical_Manual_Masonry.pdf gives the 0.038/0.043 Pavatherm nos. They seem to put at least 60 PavaPlus on the outside, then add PavaOrdinary (better insul, presumably cheaper?) behind it for thicker installations. Greenspec's giving strange figures!

k- (nowadays shd be renamed lamda-) and u- not interchangeable - u is k but with thickness added into the calc.

Can you ever do that for us Keith - fish out off-topic bits and dump into a new thread?

a certain amount of trickle ventilation is a requirement of the building regs for new build. either 4000 or 8000 mm2 per room. these are vents that are fitted through the frame, destroying the airtightness you have been working hard to achieve. the good news is that a) you can close them if the ventilation is not desired and b) they are completely secure, unlike the "night vent", open a fraction position of windows (that you are referring to as "the trickle vent effect".
the trickle vents are not taken into account when measuring U value. and they are not a requirement per window, but per room.

Long time since I specd trickle vents - Bldg Insps not given trouble, seem happy with the open-a-ctack lockable window position. And why not? - what's the difference between that and a trickle vent? Trickle vents are made cheaply, so have no chance of being airtight when 'closed'.

Ambitious extension/uprating mainly. The only venting (other than kit/bath fans) being the open-a-crack cockspurs.

Hi Maren,
Just to add to my earlier posting about aluclad costs, windows were cheaper at Broxwood than Internorm but doors were the other way round making total costs roughly the same. Haven't heard yet from Russell Timbertec or Rawington.

Haven't heard anything specific about plaster/render causing damage but my builders were wanting them towards the end of the refurb

Our quote is mainly for Miratherm windows, with system 4000 used for French doors - we've mixed and matched a bit to get the doors opening the way we want, level thresholds and so on. We're also having the frames made in oak rather than engineered timber, which adds to the cost.

Tuna: thanks for the info, I was wondering if this was some totally unknown system, but have now found details on the manufacturer's website as well. What level thresholds are you looking for? We want an external door with level threshold and french doors with level thresholds. The external door is for my utility room so I would ideally like this to be a tilt and turn door but nobody seems to be able to do a level threshold for tilt and turn doors. Probably technically impossible? I am sure the oak will look beautiful - our budget won't stretch any further after chosing wood instead of our usual PVC! But that alone makes me feel happier, I just hope the windows will really be better than the PVC we bought for our last two houses and worth the money.

valasay: As far as I know Nordwin is the brand name of Rawingtons Mira and Braga windows at the manufacturer's website: http://www.gutmann-international.com/hgw/index_en.html

This catalogue shows some (or all?) technical details of the Nordwin windows; the link is to a different website as I could only find this catalogue in German on the Hermann Gutmann Werke website.
http://www.beslagskonsult.se/downloads/catalog_nordwin.pdf

Possible to get agreement that no finger joints will be visible on the inside and/or outside face. Doesn't matter anyway in not clear-finished.

Price Update:

Rationel windows supplied by ADW Ltd in Cumbernauld: £5904 ex VAT.

The U-value for these alu-clad, double glazed windows is given as 1.4 (average), these are the only windows
built 6-22-4 with warm spacer (and argon filled).

I am quite taken with these windows, especially as the vents disappear into the frame when closed and are invisible from the outside. Have now been advised by two companies that the glazing bars worsen the U-value, whereas Nordan said no (probably the way the bars are added?) so asked for price and U-values without them from ADW Ltd for the rationel units.

Nordan: triple glazed alu-clad £6235 ex VAT.

Russell Timbertech: triple glazed all-timber £5719 ex VAT (but only with outward opening doors, not with tilt and turn inward).

Still waiting for Broxwood and Alba quotes

Tuna: thanks for the tip will try and see the windows with the local suppliers but might struggle with those further afield. Unless they send out samples?

Fostertom: we are not so bothered as we will indeed be going for either a dark stain or opaque finish but I'll keep this in mind for the future.

Monty: thanks for your concern. I posted the Nordwin catalogue in response to valasay to show that Nordwin was the particular name given by the Hermann-Gutmann-Werke to the same aluminium profiles discussed earlier (Braga and Mira) as made specifically for the Scandinavian/British market. You are right of course that this says nothing about the actual timber frame or glazing units.

We did buy from a very well known company using unsavoury practices when we bought our first UPVC windows. Lambs to the slaughter, we fell for every single marketing gimmick. The windows themselves were okay but so badly installed, ants kept walking through the gaps and the wind made very strange noises blowing through the gaps between frames and walls on one side of the house and out the other side of the house. When we phoned the company to rectify the proble (same name, same phone number) we were told the company was bought over and the warranties no longer valid. Which was not quite true as we found out later but we certainly did not take them on. We fixed the gaps ourselves instead.

Do you have any insight on the Rationel windows?

James: still waiting for the quote