Two extensions/share roof?

Wantobe

I'm thinking of doing two simultaneous extensions to two adjoining terraced houses. Is it possible to have one roof to save on cost? The houses need to remain separate internally and in the roof space.

sydthebeat

it certainly can be done, your basically building two lean-to's.

run your 215 party wall to the underside of the roof covering.

Wantobe

Thanks, Sydthebeat. I was wondering though- the extensions will be northfacing- can I slope the roofs back towards the terrace and maybe capture some sunshine from the south through a rooflight/s- with a channel for rainwater between the old and new structures or does that sound odd ( or expensive:rolleyes:)?

Mellor

The terrace will probably block most of the light so prob won't be worthwile.

If the extension will be two story, then it is possible but not something I would advise. A gull wing roof like that is achievable, but imo needs to be in a total new build. An extension increases the risk of the joint failing, the potential loss is far greater than the potential gain.

Not worth the risk imo. A north facing skylight will still let in some ambient light, but no direct light.

sydthebeat

better off createing a shared A roof with each dwelling getting a west or east rooflight, if the slopes suit existing openings.

muffler

sydthebeat wrote: »

better off createing a shared A roof with each dwelling getting a west or east rooflight, if the slopes suit existing openings.

That or a hipped roof

martinn123

What about two hipped Conservatory roof's with a structural Box Gutter sitting on the party wall.

Currently with Vista Therm Elite you can get glazing with U value 1.1m/m2K.

As its northfacing at lease the available light will get into the structure

Wantobe

martinn123 wrote: »

What about two hipped Conservatory roof's with a structural Box Gutter sitting on the party wall.

I don't even know what that is. Is it a glass roof?

martinn123

Wantobe wrote: »

I don't even know what that is. Is it a glass roof?

Yes, a standard hipped conservatory roof will have gutters on 3 sides, with two roofs side by side, the rainwater in the middle, will be collected in an aluminium box gutter which would sit on the party wall.

The roof itself, is an aluminium structure which is glazed. As you are northfacing this will allow available light into the space.

I have seen this done loads of times, the box gutter will be a special as both roofs will come down onto it, but other that that its a standard two roof structure.

Wantobe

Thanks Martinn, sounds great but not for me. I don't like too much glass overhead because of the glare factor but also I think cleaning it would be difficult.

Can you go for an A frame roof if both sides are uneven- ie one extension will be 40m but the other will only be about 25m ( sorry can't do the squared sign).

ianmurphy

It is for sure possible and the best root would be two apex roofs so that velux roof lights can allow light in. I have done it myself.

martinn123

Well if its north-facing, glare wont be an issue as you will not get any direct sunlight.

Cleaning is also not a problem , as you can use the box gutter as a platform, up to 270mm wide, and a yearly wash down will clear any debris. You can also walk on the glazed panels as they are designed for this.

anyway glazed roofs are not for everyone, just made the suggestion as light seemed to be one feature you were concerned with.

No real issue with the different sizes, both roofs are designed individually to suit the location, the common factor is the box gutter on the party wall.

ianmurphy

you could also share the party wall to save money and have no gully??

Mellor

martinn123 wrote: »

anyway glazed roofs are not for everyone, just made the suggestion as light seemed to be one feature you were concerned with.

It would let in more light than is needed and piss out lots of heat.
A glazed roof on the north side is a pretty poor suggestion

ianmurphy wrote: »

you could also share the party wall to save money and have no gully??

All party walls are shared, there is no such thing as a non shared party wall.
a shared roof is a simple issue, all this talk of glazed roofs, double apex, box gutters is really making it way way more complicated than it needs to be.

martinn123

Mellor wrote: »

It would let in more light than is needed and piss out lots of heat.
A glazed roof on the north side is a pretty poor suggestion


a shared roof is a simple issue, all this talk of glazed roofs, double apex, box gutters is really making it way way more complicated than it needs to be.

I made one suggestion, and my subsiquent posts were replies to questions asked by the OP. Would you prefer that I did not reply to a question.

As to pissing out lots of heat I quoted Vista Therm Elite Glass with a U value of 1.1. If thats not good enough we could discuss triple glazed.

While I appreciate your opinion that a glazed roof, is a pretty poor suggestion, at least the space will get some light.

Yes a shared roof is simple, so is exploring/discussing alternatives if only to consider them, and in the end going with the two lean to, and a shared wall.

Wantobe

I like the idea of the glazed roof, though and because it is north facing it ( to my uneducated brain) is more appropriate than in a south facing direction as I would hate the glare/it being too bright. I saw a link to an orangery on a website that looked pretty cool.

But all things considered I think I'd go for a normal roof and lots of insulation. Just trying to get an image of it but I'll definitely be getting plans drawn up by a professional.

Mellor

martinn123 wrote: »

I made one suggestion, and my subsiquent posts were replies to questions asked by the OP. Would you prefer that I did not reply to a question.

As to pissing out lots of heat I quoted Vista Therm Elite Glass with a U value of 1.1. If thats not good enough we could discuss triple glazed.

While I appreciate your opinion that a glazed roof, is a pretty poor suggestion, at least the space will get some light.

Yes a shared roof is simple, so is exploring/discussing alternatives if only to consider them, and in the end going with the two lean to, and a shared wall.

Of course I wouldn't perfer that you didn't reply to the question. You are completely free to do so.
Just as I or anyone else is free to voice their opinion if a suggestion is a bad one in their opinion.

I am aware that you quoted a u-value of 1.1
Which isn't very good at all. It's good compared to other windows and glazing, its terrible compared to other roofs.

martinn123

Mellor wrote: »

Of course I wouldn't perfer that you didn't reply to the question. You are completely free to do so.
Just as I or anyone else is free to voice their opinion if a suggestion is a bad one in their opinion.

I am aware that you quoted a u-value of 1.1
Which isn't very good at all. It's good compared to other windows and glazing, its terrible compared to other roofs.

In their opinion, used twice in this sentence, to make up for its omission from your first post.

Yes 1.1 is not great, triple will get it down to 0.7, and still let in light.

Wantobe wrote: »

I like the idea of the glazed roof, though and because it is north facing it ( to my uneducated brain) is more appropriate than in a south facing direction as I would hate the glare/it being too bright. I saw a link to an orangery on a website that looked pretty cool.

But all things considered I think I'd go for a normal roof and lots of insulation. Just trying to get an image of it but I'll definitely be getting plans drawn up by a professional.

Discussion, sharing thoughts, opinions, and finally, a decision having taken advices offered into account, thats what its all about.

Mellor

martinn123 wrote: »

In their opinion, used twice in this sentence, to make up for its omission from your first post.

It's clearly a typo (from editing)
I'd advise you to drop the attitude

Yes 1.1 is not great, triple will get it down to 0.7, and still let in light.

You are still missing the point, no glazing has a good u-value compared to a egular roof. The situation above is the worst location and condition for glazing. Overshadowed and to ther north, I don't see why you can't see that.
THe lower the u-value the less light that will be let in.

martinn123

Mellor wrote: »

It's clearly a typo (from editing)
I'd advise you to drop the attitude


You are still missing the point, no glazing has a good u-value compared to a egular roof. The situation above is the worst location and condition for glazing. Overshadowed and to ther north, I don't see why you can't see that.
THe lower the u-value the less light that will be let in.

What you dont get, is that I agree with most of your opinions. Having worked in the glazing business for many years I am aware of the realities of a glazed north facing roof.
A query was raised as to the lack of light, with a stardard roof, and in THAT context I made a suggestion, to be ignored, or otherwise, but just that a suggestion. The OP stated he likes the idea, but will go with a standard roof, fine with me.

I think u value measures insulation values and has no relevance in light, light transmission has a different measure, can't remember what it's called, maybe someone will enlighten me. your above statment is confusing.

Mellor

martinn123 wrote: »

What you dont get, is that I agree with most of your opinions. Having worked in the glazing business for many years I am aware of the realities of a glazed north facing roof.
A query was raised as to the lack of light, with a stardard roof, and in THAT context I made a suggestion, to be ignored, or otherwise, but just that a suggestion. The OP stated he likes the idea, but will go with a standard roof, fine with me.

I think u value measures insulation values and has no relevance in light, light transmission has a different measure, can't remember what it's called, maybe someone will enlighten me. your above statment is confusing.

There's nothign wrong with the suggestion. I was stating why I thought it was a bad one (the orientation and location). You appear to have taken this personally.

I'm not surprised you work or worked in the glazing business given your posts. But I am surprized that you are confused by the second statement.

I'll explain.
The light allowed in (as well as the solar gain) from an opening is called the visible light transmittance or VLT. As u-values for glazing systems decrease, so do does the VLT. Which simply means highly insulated glass with more layers (of glass, films and coatings) let in more light and heat.

Hopefully that clears everything up

martinn123

Mellor wrote: »

You appear to have taken this personally.

I'm not surprised you work or worked in the glazing business given your posts. But I am surprized that you are confused by the second statement.

I'll explain.
The light allowed in (as well as the solar gain) from an opening is called the visible light transmittance or VLT. As u-values for glazing systems decrease, so do does the VLT. Which simply means highly insulated glass with more layers (of glass, films and coatings) let in more light and heat.

Hopefully that clears everything up

Hi, dont worry about me taking things personally, the way things are in this industry, indeed many industries, means I have more to worry about than a reply to a post of mine.

I am confused because there is little relationship between better insulated glass and VLT.

From a chart available on www.careyglass.com/architectural/downloads
you will note that the addition of Tinted Glass, bronze, grey, blue etc does effect VLT, but for clear glass the readings are.

6mm clear/16mm air/ 6mm clear VLT 80, U 2.8
now insulate
6mm solar neutral/16mm argon/6mm clear VLT 70 U 1.1

so a reduction of 250% in U Value only produces a 14% reduction in VLT.

The addition of an extra sheet of clear glass to triple glazed, will again not reduce in direct proportion, the amount of light transmission.

With Tinted glass you can reduce the VLT to 36 ( grey tint ) but the U value remains at 1.1

So that's why I was confused by your statment

Hope that clears the matter up

Mellor

Where I said they are directly proportional?

I said as U-value decreases, so does VLT. You have just proved my point for me with the data above.