Glazing in new extension

[KelvinM]

Hello everybody

I have recently got LBC for some work on my 300yr old Listed cottage. The main works will be as follows:

(A) A single storey extention to the kitchen;
(B) A two-storey extention to the back of the house (replacing a very poor quality "lean-to" circa-1970).

The single-storey extention in (A) is going to be quite modern. For example, one corner of the room will totally open from floor to ceiling into the garden and will have a rooflight forming most of the roof. The CO liked the idea of the modern addition as it shows the house developing over time. Both the rooflight and opening will have slim double-glazed units.

The two-storey extension (B) is replacing a poor quality lean-to but is going to be bigger in terms of height and depth. At the moment the CO wants traditional leaded single glazing in the windows in this extension. I am happy with this to and extent, although I am want to think of other options that I could propose. My main concern is energy efficiency - my heating bills are quite high and in the winter (from Nov - Mar) the house never gets warm (apart from the lounge when the open fire is burning).

The way I see it is there are 3 options that may or may not be acceptable:

(1) Go with traditional single glazing. If this is the case, does anybody know of and glass or coatings that can make these marginally more efficient;
(2) Slimlite glazing incorporating traditional leaded panel, although I'm not sure whether the CO will got for this;
(3) Single glazing with secondary glazing. I am not sure about the look of the secondary glazing.

I have had conversations with the CO regarding the bricks we wish to use and the stance was that he didn't want new bricks that looked old or reclaimed bricks. The reason for this was to avoid giving a misleading impression as to the age of different parts of the house. I find this at odds with the stance taken on the windows in the two-storey extension.

Given the experience of people on this forum, I was wondering whether anybody had any options on the situation or any experience of the three glazing options that I have listed. Or indeed, if there are any options I've missed.

Thanks.

 

[Penners]

Given that you'll need to satisfy your CO, I suggest that you should put the three options to him/her.

But for what it's worth, I would go for option C. Just be sure that any glazing bars/structural components of your secondary window run in line with those of the primary, for the most aesthetically pleasing effect.

 

[lou]

Kelvin - try the GreenBuilding Forum. I have been told that Pilkington's have a new thin profile glass that is more thermally efficient than normal glass. Someone on that site is sure to know the name of it. You could try searching under Pilkington. Or just google Pilkington maybe. Good luck. We may, eventually be looking to do something a little similar so will be interested to hear if it works for your CO.

 

[KelvinM]

I spoke the the CO and it seems like secondary glazing is acceptable. What was interesting was the he told me that LBC was not required to install this which surprised me given that I have seen LBC application in my area for such work. It was stressed though that this would apply to non-uPVC secondary units. Slimlite didn't receive a warm response. I think this is more to do with preference in the local authority as I am fairly sure that they have been used in other areas.

 

[biffvernon]

Kelvin, this bit with the windows is new build? And your main concern is energy efficiency? And the CO, very sensibly, likes a distinction between old and new?

Don't even think about Slimlite - they are for odd situations where you are trying to squeeze into a slim place and don't care about the cost.

Secondary glazing is not going to give the energy efficiency you are looking for.

So go for double glazed sealed units 4-16-4mm with argon fill and low-emissivity coating and insulated spacers. Or better still triple glazed, say 4-12-4-12-4, or even 4-16-4-16-4 again with argon and low-e coating.

Anything less and you will probably fall foul of Part-L of the Building regulations, which I suspect will apply to this new extension even if they don't to the old part of the listed building. ANyway, it makes sense and your comfort will increase/fuel bills be lower.

 

[KelvinM]

Kelvin, this bit with the windows is new build? And your main concern is energy efficiency? And the CO, very sensibly, likes a distinction between old and new?

That is correct - there are two extensions. One it totally new and the CO is happy to have double glazing. This is sensible as most of this structure is glass (glass doors opening up a corner of the room into the garden, plus a large rooflight). The second extension is new, but will be replacing an old lean-to and will be much bigger. I was just a bit surprised that the CO was happy with modern windows in the first extension, but insisted on single-glazed windows in the replacement extension with real leaded glass. The current lean-to has single-glazed windows but no lead.

Regarding the Building Regs, my architect assures me that even with single-glazing there should be no problems. I'm not convinced, but await the results of the SAP calculations. Unfortunately the architect didn't do the SAP calcs before putting in the regs application (which I was slighly surprised at given the amount of glass in the structure and the fact we are using single-glazing on one part). Building Control have asked for the calcs as a condition.

 

[Joiner]

Bif is right about Slimlite units. Their cost is ridiculously high and I have heard two bad reports about their reliability. They also never got back to me when I asked about their units achieving the higher spec required to meet the new Part L Regs, which further undermined confidence.

For the new part you will, as Bif says, need to meet Regs. Also, given the uncertainty about how the new Parts L & F are going to be applied, in terms of proving that everything possible has been done to improve energy conservation in an old building without compromising its historic character, notwithstanding the LBC (despite its predating the new Regs) a word with the BCO might be wise, unless you have it in writing from the CO that what THEY are willing to accept/insist on satisfies the BCO. In fact, it might be wise to get that piece of paper anyway. I suspect that the whole matter of the new Parts L & F and how they're applied to older properties will be just another postcode lottery. A response to a query on another forum by a Senior BCO appeared to confirm that likelihood!

 

[christianb]

Personally, I'm with Penners on the secondary glazing solution. Sure, as Biff says, they're not quite as good as top-notch dg units, but from an aesthetic point of view, single glazed windows do look more the part.

And you'll never live long enough to recoup the outlay on double glazing in saved energy.

 

[biffvernon]

That's true enough if the old glazing is going to be retained but I gather in this case there will be new glazing and secondary glazing - so it will be expensive and energy inefficient. Still, it might be a good thing in some situations where the character of the building is of imprtance.

I like leaded lights. They are good fun to make.

 

[Penners]

you'll never live long enough to recoup the outlay on double glazing in saved energy.

I fear that's also true of secondary glazing.