Is this canopy for my front door OK or need some further work?

[lozcozard]

Hi.
I want to build a front door canopy. I am at the planning stage and wondered if anyone could give some advice. The Sketchup plan is attached. It will be 2.5m wide by 1.5m deep. I'll tile the roof to match my house roof tiles.

Some specific questions I have are:

1) Should I put another beam in the back? I dont think I need it if I secure the back rafters to the house wall

2) Do I need a ridge beam or board? Or could I just connect the end of rafters together as per the design and put purlins in between to keep them in place? I may use OSB on top which would secure them even more. The angle between top of rafters is 120 degrees to match my roof angle.

3) Do you think a 4x4 post beam is good enough out front or too thin? This is more a visual appeal not structural. I think a 6x6 would be me more "grand" but my supplier is charging £39.40 for an 8 foot 6x6 compared to £14.60 for an 8 foot 4x4. I'll need at least 6 of them (using 2 horizontals for the rafters to rest on) so cost is adding up then.

4) Do you think a 2 x 4 for the rafter tie is ok? Again more of a visual appeal than structural. I have seen designs using the same size timber as the posts, again adds to the grandness of it, but if I do go for 6x6 its another £39.40. I am not sure if the width of the beam will contribute much, so maybe even a taller beam, a 2 x 6, would make it look a bit more grand, still costs a lot less than a 6x6.

5) Do you think the rafters need a birdsmouth cut? I thought just rest it on the beams, I'll use some kind of brackets to keep them in place of course.

6) Lastly, I am not bothered about fancy finishes on the wood, or curving wood as seen in lots of canopy images online. So as you can see its a simple design, I am just hoping it will still look good once finished! Any thoughts on that?

Thats it for now!

Thanks

 

[Deleted member 174758]

You don't need a ridge if you are using sheet material to clad your roof, but if yo do withoutvthe ridge, howxare you going to fix your rafters together? You also need to temporarily tie the rafters from benesth whilst you assemble it all

The 4 x 4 posts by the wall could be reduced to 4 x 2s, or possibly got rid of completely if you could tie the roof bearings into the masonry. I think that you need to tie the front of the frame together by adding a connector betweeen the two roof bearings (not the rafters as at present), otherwise I feel the frame might spread over time.

If you don't want to birdsmouth maybe consider truss clips instead. Fix in place with twist nails. Sorry, but as a chippy I think that birdsmouths are better, but they are more difficultvto achieve. Nail rather than screw the structure together in most places - nailed structures often resist wind buffeting better than screwed ones

 

[lozcozard]

Thanks for your reply.

I thought I could just use a flat bracket across the top ends of the rafters to secure them. Then the purlins would stop them leaning. Although probably not a big deal to add in a ridge beam if it’s easier. Does the beam need any vertical support? There won’t be any in the back, I’d have to secure it to the house wall somehow.

the tie on the front would be screwed to the frame/supporting beams to stop them opening up. Then the from rafters screwed to that also.

I’ve built another flat/sloping roof canopy and on that I used hurricane clips on the rafters so thought something similar here instead of birdsmouth. I’d still have to use similar fastenings anyway with birdsmouth wont I to stop the spread wont I? Unless I have a tie on every rafter.

 

[Deleted member 174758]

I thought I could just use a flat bracket across the top ends of the rafters to secure them. Then the purlins would stop them leaning.

How exactly were you intending to install the rafters? If you erect a temporary framework (basically a couple of inverted T-frames) to support the ridge, then the rafters can be individually cut and fixed onto the ridge. It is also a lot easier to measure and cut birds mouths, which does away with the need for truss clips, angle brackets, etc as they could simy be cross nailed into the "ring beam" (I won't call it a purlin because I was taught that purlins are always mid span). Doing it the way you show all of your timbers will need to be assembled before lofting them - and they will all need to be tied in some way, like a truss roof frame, to stop them falling apart because a join at the apex will possibly have insufficient strength.

Does the beam need any vertical support? There won’t be any in the back, I’d have to secure it to the house wall somehow.

Only whilst you are erecting it. After that it is suported by the rafter ends, which must meet each other to avoid a "snake back" ridge over time. Either way i think it is still advisable to diagonally tie the rafters on the underside to give more rigidity during the cladding of the roof with the sarking board

The tie on the front would be screwed to the frame/supporting beams to stop them opening up. Then the from rafters screwed to that also.

Given that you are installing sarking boards, possibly a membrane, battening, tiling and ridge tiles I think you are asking a lot from a single small tie. As I said I think I'd reduce or remove the uprights at the wall (they could be replaced by corbelling or pocketing-in) but instead of a tie at a high level above the "ring beams" at the side I'd use a proper fill size tie across the front of the structure, half lapped, to form a 3-sided ring beam. That will stop any spread at the front of the structure. It will be even better if you cut a tenon at the top of the posts which passes through a square mortise in the half lap joint - that way you aren't dependent on mechanical fastenings (like screws, which are generally a bad idea on roof structures) which can fail as tbe result if wind and corrosion

I'd also be considering protection of the front of the structure by adding an extra frame at the front, overhung by 150 to 300mm and ladder framed onto the last pair of rafters.

I’ve built another flat/sloping roof canopy and on that I used hurricane clips on the rafters so thought something similar here instead of birdsmouth

Why are you so opposed to birdsmouths? They provide a flat connection area which enables a roofer to cross nail them onto a ring beam or wall plate without the need for additional fastening plates. They also avoid a point load on the edge of the ring beam which in turn reduced the liklihood of partial failure at that point should rot occur.

I'm beginning to think I should redraw this in SketchUp. Give me a day or so to sort my nee laptop out and maybe I'll have the time

 

[lozcozard]

Thanks for the detailed reply. I was just wanting the easiest solution for me but not if it affects strength or safety. So I’ve since thought that I would install a ridge beam. If I put a horizontal beam at the back and then a vertical in the middle of that, so same as front, I could support the ridge beam for assembling the joists.

And since posting I have found some designs where I can see that cross nailing/screwing through the birds mouth so think I may give that a go too.

I was going to redraw my sketchup. I’ve found a design I liked I thought I might try to replicate. Most I see online have extra features I didn’t really need so was trying to see what I could leave out and make it simpler.