Glass Vs Heat loss

last year

Hi All,
We are planning a renovation on our 1930s semi detached house. We've planned a big kitchen/dining/living space and have lots of glass to make the most of the views and capture the light. Currently we've got almost 2 walls of glass - we've asked for as much as we can for planning purposes but not completely sure on whether we should keep it all. We realise that of course more glass would be more expensive and we are taking this into consideration. What I'd like to ask is about the heat loss/insulation side of things. I'm not sure how to strike a good balance between the glass and heat loss - I've read a bit about SAP assessment and heat loss experts - should we be thinking about this as our next step?
Any tips or advice would be very much appreciated!

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Comments (5)

tamp75
last year
Hi, I’m sorry I don’t know anything really about heat loss but I’m sure the companies who produce the large windows and doors use thermally efficient glazing. However, depending on where you live and the direction of the house, I think that you may also need to consider what you are going to do about heat gain. After this summer’s heatwave and the prediction of hotter weather to come, such large walls of glass can create massive heat gain inside, unless properly planned for. I imagine there may be similar options with glazing to reduce heat gain but also consider shading directly outside of the doors, eg a canopy, pergola, etc.
Katie Duke
last year
Like the earlier comment I don't know too much about this in any professional capacity but my first thought was also solar gain. Depending on the orientation you could end up with something incredibly warm possibly unbearably hot as well as cold in winter months. Are you having roof lights/veluxes as well? That's another consideration. Things I would think about would be triple glazing and creating some kind of external shading on the windows (brise soleil/pergola type affair).

I would really plan for window treatments blinds and curtains - will be expensive with so much glazing - but plan from the beginning to get a neat look. Blackout type builds for insulation quality preventing both heat loss and gain and then also maybe something gauzy to diffuse daylight plus heavier curtains for evening time. It's no fun sitting in a cold room! For example you could look at recessing blinds into ceiling etc or some kind of track that allows for multiple blinds, panels, curtains etc. I would also consider whether you could use a smaller amount of glazing but to frame a particular view/s. This would give you a bit of wall back for radiator/art/bookshelves. The plan looks like a fantastic amount of space, good luck with everything!
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Hi John! I've just noticed your message, we are away on holiday atm (lucky you, it's cloudy today so I have time for Houzz :))). I'll try and answer your questions to the best of my knowledge, but before I even start, have a look at this ideabook - I gave some details on our system in the comment section there. https://www.houzz.com/magazine/warm-up-your-bathroom-with-heated-floors-stsetivw-vs~18303936 Ok, so we have a hydronic system throughout the house, no radiators at all. We agreed with the builder to use the original floorboards as the base and add joists/ beading on top to support the aluminium sheet and pipes (see the photos in the ideabook), as the height of the rooms could take a loss of some 10cm. In the (extended) kitchen and basement, they first laid down thick insulation boards, then the pipes, then poured screed on top. They insulated all the ceilings (or floors!!) and used plasterboard with foil on it to ensure maximum heat radiance. At our request, they also 'hung' pipes on the (basement) ceiling underneath the original Victorian mosaic tiles, so the entrance hall gets heated that way too. Except for one bathroom (where we used limestone) the other bathrooms, kitchen and basement have ceramic tiles. The limestone is cracked now, after 18 months since we moved in - fortunately it doesn't look too bad; no issues with the ceramic tiles. We went for engineered wood in the rest of the house - they used some special glue that allows movement. I have no idea how many zones we have, there are 18 thermostats in the house (I remember that from the invoice :)), each in every room and halls/ landings. I know that because our kitchen is quite large, they used two circuits to cover the room efficiently (but one controller/ thermostat), same in the master bedroom. At the time, we researched and discussed a lot about environmentally friendly alternatives to gas/ electric boiler - however, living in the middle of Cardiff with only 50sqm garden, we were very limited in our options. We also considered solar panels, but couldn't get planning consent, as we live in a conservation area. One more point: our last house was roughly the same size as this one, but heated with radiators on a combi boiler - our gas-electric bill is now two thirds less than it was in the old house. I'd say go for it! Research what works best for your house, discuss with the installers - some are very knowledgeable and helpful and do it! I honestly love our home and don't think I ever want to live somewhere with radiators again! Hope this helps - good luck!
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If you're leaning more towards a pitched roof, perhaps you could extend your glazing right up into the gable to maximize the light coming in. I've attached a couple of images of projects where we have done just that. The first was necessary due to it being a listed building so we suggested an additional tiled roof would be more in keeping than, for example, a flat roof with a roof lantern. The second was on a lovely Victorian terrace in Coggeshall and again, we suggested echoing the original architecture with a pitched roof and glazed gable. If you would prefer an orangery style extension, despite some previous comments it is definitely possible to have a space that is a nice even temperature all year round, doesn't collect lots of flies and doesn't leak. We have built these for 30 years. All of our roof lanterns are available with solar controlled glass and motorised vents, plus the combination of masonry and glass (as opposed to a traditional conservatory which is mostly glass) provides a a more consistent room temperature anyway. We offer a 10 year guarantee on our joinery, glass and paint coatings (parts and labour) - that's how confident we are that it won't leak. We also use Accoya wood in our products which is incredibly durable, stable, moisture resistant, fungus proof, inedible to insects and thus incredibly low maintenance. It's definitely worth googling Accoya if you're considering going for a structure that incorporates timber joinery.
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Becci C
last year
are you working with an architect?? we had 4m wide bifolds and a really large skylight in our new extension. the architect had to do some calculations to check it was going to pass building regs, if not we would have needed something to offset the heat loss, I can’t remember exactly but it was maybe a different type of insulation or construction.
our calculations came back fine but there were definitely ways round it if it hadn’t.
123
last year
We have a lot of glass in our extension and had to have a triple glazed roof to pass building regs. We find heat gain is actually a bigger issue than heat loss. If we did it again we would either have less glass or use recesses/overhangs/external shading to manage that. We don’t have window treatments and have lit the garden so we aren’t looking at a cold black wall at night. We still love ours but it could have been done better, make sure you quiz your architect or builder about all these issues.
PRO
Absolute Project Management
last year
I would second comments above;
1. Building regulations require that if the glazed area is greater than the equivalent of 25% of the floor area of the extension, you have to justify it by upgrading the u-value (measure of heat transfer) of the windows and/ or other thermal elements. There is a calculation involved for which we'd recommend engaging an architect or other specialist.
2. Solar gain (heating) from large South & West facing windows can be a big problem, especially with likely ongoing hot summers. Overhangs for external shading is an option to mitigate this.
We've written a bit about this in this journal post on efficient homes; https://absoluteprojectmanagement.com/efficient-homes-improving-energy-and-water-use/

Glass Vs Heat loss

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tamp75

Katie Duke

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