modifying exisiting roof

[gg23]

hi,
the images below show the existing roof plan (left) and the proposed roof plan (right). The new roof will be made using trusses and is a simple gable end roof. My concern is around the demolition of part of the existing roof. Can the existing roof simply be severed at the point where the new roof will be placed? Doesnt the exisitng roof frame need some type of bracing? There is no mention of this issue anywhere in my engineers or architects plans.

Thanks
greg

[echnidna]

is the roof being severed over a wall

[journeyman Mick]

I'm guessing that one of the excess common trusses would be tacked onto the first truss of the new section to take the ends of all the battens of the existing roof. Is the new roof an extra storey addition? I'm guessing/hoping there is a height change, otherwise I don't know what's going to happen to all the runoff from the valley gutter and the section off roof that butts into the new. If the new roof is at the same height on the top of the wall you'll need a box gutter at the junction. Box gutters should be avoided wherever possible as they're a potential entry point for water (lots of it!) into the interior of your house. As the remaining roof will still have a few hip ends it should be pretty much self bracing. Any half decent builder or carpenter should be able to marry the two roof sections together, you just need to resolve the runoff issue (if any).

Mick

[gg23]

It appears not to be over an existing wall. The point at which the old roof will be cut is to the right of an internal non-load bearing wall and to the left of a section of an external wall. I have included a new diagram showing the detail. The solid black line is where the old roof will be cut.
greg

[Brickie]

Box gutters should be avoided wherever possible as they're a potential entry point for water (lots of it!) into the interior of your house.

Mick

I would avoid box gutters like the plague, I havent seen or heard of one that didnt leak.

[gg23]

No, the roof is to allow for the ceiling level to be the same in the laundry, so yes there i a height change for this room only. The roof itself will be at the same height on side (the bottom on the diagrams) and higher on the other side.

I appreciate that there will be some issues with gutering and so on where the two roofs join, but at this stage my main concern is the structural integrity of the existing roof when it is cut.

thanks for your advice
greg

[echnidna]

are you doing the job or are you getting a tradesman to do it?

[gg23]

I am doing it with the help of a tradesman/friend

[ausdesign]

Do you have any elevation drawngs - i'm having trouble getting my mind around how that's going to work.

[journeyman Mick]

Is the existing roof a hand pitched roof (ie rafters, underpurlins etc) or a truss roof. If the latter, there won't be any structural issues. If the former, you'll need to work out what bracing will remain once you cut the roof back and whether you will need extra bracing. I'm guessing that this is the case. BTW, don't underestimate the guttering issues, in my opinion these will be much harder to resolve than any roof bracing issues. There's no way on earth I'd ever build a box gutter into my place and that's the only way I can see you marrying the two pitches together.

Mick

[gg23]

hi mick,
Existing roof is hand-pitched. How do we determine if the roof will need extra bracing?

Regarding the guttering, on one side (the western section of the roof) the old roof line matches the new roof line, and to make things more complicated the old roof is tiles and the new corrugated iron. I have been told to provide sufficient overlap.

On the eastern half of the roof the new section is higher than the old.

greg

[gg23]

elevations

[memphis]

when we did our extension the guys just put in a couple of extra supports to hold up the existing roof

its pritty simple, if theres something hanging once you cut it with nothing holding it up, support it.

you WILL need to do some bracing. but it wont take any major effort.

[echnidna]

but the supports need to go in the right place

[gg23]

thanks again for the advice, my main concern was that given that the roof has bull-nose at either end, then I assume the main ridge beam connecting will be in compression. So if i cut it down the middle say, will the remaining bullnose section be pushing whats left of the ridge beam. I was thinking of some type of tensioning to counteract this. I could be just being overcautious?

greg