Building a Gable Roof over existing Deck.

[Inspector]

Hello everyone. This coming week, I'm hoping to start building a gable roof over our existing deck and I have a couple of questions.

Before I ask them, I'll get the particulars out of the way:
•The deck is 20'x16' (Total Span of roof will be 20')
•Roof Pitch 4:12
•Assisted building a gable roof on a friends shed before and I also built the deck this roof is going on.

Questions:
1. How do I attach the Ridge Beam to the house? Should I have some sort of ledger to attach to or just nail it into the side of the house? (I'll be removing the vinyl siding first). I figure, that the house really isn't providing the support for the Ridge beam (the rafters are, right?).

2. Will a J-channel suffice, or should I have the flashing (or both)?

3. I read in another post, that if the span of the roof is greater than 12' then collar ties are useless. Is this true or did I perhaps misread this? Is there another alternative? I'm trying to maintain a cathedral ceiling.

4. If the alternative to 3 is engineered trusses, does anyone have a ballpark figure on the cost/truss?


Thanks for any help that you can give! :D

[mjpliv]

1 - If you are using a ridge BOARD then you can just tack it to the side of the house to hold it's position while you place the rafters. If you are building a ridge BEAM roof then the beam needs at least 3-1/2" of bearing which must be continuous to footings. For the rest of these answers I will assume you are building a ridge BOARD roof structure where the rafters press againts each other for support.

2. If you are refering to the flashing between the new roofing and the old siding material then you require a step flashing of some sort. Most building supply stores will carry this in pre-cut lengths or you can buy a 10" or 12" rool and cut your own. Make sure your wall air barrier extends down over the flashing.

3. You need to restrain the ends of the rafters regardless of the roof span.

4. I would quess (and its just a guess) that you would pay between $50.00 and $75.00 per truss.

[Inspector]

Yes, I'm refering to a Ridge Board. Sorry.

When you say "restrain the ends of the rafters", I'm assuming you mean having the birdsmouth nailed onto the outside beams (sill plate?).

Other than than, I think you covered my major concerns. Thanks.

[mjpliv]

Restraining the ends of the rafters refers to keeping the rafters from pushing outward when the roof deflects. This means you have to use some sort of collar tie or ceiling joist. Attaching to a top plate only provides vertical support unless the top plate itself is laterally supported along its entire length.

[rodster]

I'm making plans to start a project of the same dimensions as this. I have a window above where my roof will go and have about 11ft 7in. of room based upon where the existing (to be removed) bay door roof ends. A couple of questions:
can I get a 4/12 pitch out of this? Will I need to drop the side wall to about 7ft10? At what height should I put the ridge board to enable the sheeting and shingles to stay under the 11ft7in mark?
Other details: planning 2x6 rafters at 16 in centers, 1/2in ply wood sandwiched between two 2x8s for a ridge board (would like to run my wire for the ceiling fan between the 2/8s and cap with a 1x4 to hide the wire.) Planned sheeting would be 1 piece of ply bead facing down with OSB on top to hide the roofing nails from the porch view. Each layer of sheeting covered with felt. Top layer with shingles.

Anything else I should be aware of?

Thanks

[doyle]

On a 16' wide room with a 4/12 pitch, you should have about 7" left over before you reach your maximum.

This is calculated by the following:
1) 32" rafter height (4" rise x 8' span=32")
2) 92-5/8" studs
3) single 2x4 btm plate
4) double 2x4 top plate
5) 1-1/2" allowance for the 2 layers of decking and for shingles

All of that adds up to just under 11'.

Somebody else please check my math...lol

[rodster]

Thanks. My roof will actually be a 20 ft span. But I get the idea. I can just add 40in. instead of 32in. But do I need to add the remaining width of the 2x6 after cutting the bird's mouth?