Post spacing.

[DaG56]

Hi all.
Im looking to attach a carport type of structure to the side of my garage. I'm going to roof it with twin wall polycarbonate.
It will be 4.8m long, 2.1m wide and be attached to the garage on one side by a ledger board. The other side I'm using 100mm x 100mm fence posts which will be about 2.1m high. They will be attached to the concrete floor by fence post anchors for concrete.
Four self tapping concrete fixings in each one. The ledger board and the facia across the top of the posts are 140 x 47 timber.
I thought 3 posts, one each end and one in the middle at 2.4m would be ok. But having laid them out they look a bit far apart. I'm not sure whether to add a fourth post which would put them at 1.6m spacings. Or am I being a bit paranoid and one post in the middle will suffice. Thanks for any advice.

 

[Deluks]

4 sounds about right here.

 

[stevie888]

I'd do 4

 

[tony1851]

I'd do 2.

 

[DaG56]

I was going to do three and with the facia boards I have being in 3m lengths they would join nicely over the centre post. Four looks a bit close together so I'm still not sure what to do. Is it likely to be a bit weak with just three? Those who've said four is there any particular reason? Or does four just seem safer? I've had a look online for anything about the structure of this kind of thing but found nothing.

 

[Dereekoo]

What looks weak with 3, the span of the facia board or the amount of supporting fence posts

 

[DaG56]

What looks weak with 3, the span of the facia board or the amount of supporting fence posts

I don't think it looks weak. It was just that 8 feet apart looked a bit of a span. I was wondering if it was likely to be weakened by having three posts. Would Three be enough to support everything in windy conditions?

 

[Harry Bloomfield]

Cantilevered.

 

[Atgni]

I have done stuff in the nice weather an thought this is a bit OTT but then when we have a nasty storm I am thinking - so glad I built it like I did !

 

[tony1851]

I don't think it looks weak. It was just that 8 feet apart looked a bit of a span. I was wondering if it was likely to be weakened by having three posts. Would Three be enough to support everything in windy conditions?

8ft apart wouldn't be a problem; a 6x2 would easily support the polycarb and snow load with minimal deflection.

What matters with an open carport is not the number of posts, but the wind uplift. Apply a few more fixings between the polycarb and timber than the manufacturer advises, and ensure there is a good fixing between the fascia and the posts (halve the posts and screw through both - perhaps consider a 75 wide steel plate as well) and ensure good resin-based fixings to the concrete.

My suggestion of two posts was not tongue-in-cheek but would look more 'designed' and neater ("less is more" etc) and also offer less posts to bump into after a late Saturday night out. The fascia would cantilever about 4ft each end (there's an optimum cantilever to reduce stress but I can't remember it offhand) and it would look good.

But whether you choose 2, 3, 4 or 24 posts, what matters most is securing the polycarb against uplift.

 

[DaG56]

8ft apart wouldn't be a problem; a 6x2 would easily support the polycarb and snow load with minimal deflection.

What matters with an open carport is not the number of posts, but the wind uplift. Apply a few more fixings between the polycarb and timber than the manufacturer advises, and ensure there is a good fixing between the fascia and the posts (halve the posts and screw through both - perhaps consider a 75 wide steel plate as well) and ensure good resin-based fixings to the concrete.

My suggestion of two posts was not tongue-in-cheek but would look more 'designed' and neater ("less is more" etc) and also offer less posts to bump into after a late Saturday night out. The fascia would cantilever about 4ft each end (there's an optimum cantilever to reduce stress but I can't remember it offhand) and it would look good.

But whether you choose 2, 3, 4 or 24 posts, what matters most is securing the polycarb against uplift.

Thanks for that tony and I did think you were joking with two.

The long side where the posts are going is almost up against a fence that is higher than my carport. So that side is protected against wind to an extent.
I'm calling it a carport but it's not actually a carport as there is a wall at the front end with a gate in it so impossible to drive a car under it. So that end has some protection against wind as well. It's just a wide path down the side of the garage into the back garden that I'd like to cover over. It's kind of like the picture I've linked.

I'm not sure what you mean by halve the posts and screw through both. Do you mean notch the posts and sit the facia on the notch?

I like the idea of setting the posts in with the facia cantilevered off them. It would look good as you say. But it's not at the front of the house and is only seen by me. So while I want it to look neat I'm not bothered about it looking fantastic.

There's one other thing I meant to ask. The ledger board is being attached to the garage facing bricks under the gutter. The bricks have a frog in them. What would be the best fixings to use to attach it?

 

[JohnD]

Mine is 6 metres long and I have 4 posts. The two inner ones have two 45 degree diagonals to the top beam in a sort of Y shape. The one at the front has a diagonal at the same angle and height to match. Apart from spreading the load, to my eye it looks more satisfying, somewhat modelled on half-timbered houses. I don't know the correct carpenter's term.

I set the posts so that none of them could be hit when opening a car door.

 

[DaG56]

Mine is 6 metres long and I have 4 posts. The two inner ones have two 45 degree diagonals to the top beam in a sort of Y shape. The one at the front has a diagonal at the same angle and height to match. Apart from spreading the load, to my eye it looks more satisfying, somewhat modelled on half-timbered houses. I don't know the correct carpenter's term.

I set the posts so that none of them could be hit when opening a car door.

I'm going to use 47 X 100 for the rafters. So I thought I'd use offcuts to make gussets across the top corners between posts and facia. The inside post or posts I'll put one each side like yours to form a Y.

I'm looking at videos on YouTube from builders and people who have done a job like this to get ideas. I recently retired after working a lifetime as a sheet metal worker and welder. So now I'm catching up with all those little jobs around the house I put off till tomorrow. I'm pretty decent at woodwork and have plenty of tools, but know very little about structural work. Or as my daughter says "all the gear and no idea".

 

[stevie888]

. Or as my daughter says "all the gear and no idea".

Good line to remember when it's "Dad can you..."

 

[Deluks]

There's one other thing I meant to ask. The ledger board is being attached to the garage facing bricks under the gutter. The bricks have a frog in them. What would be the best fixings to use to attach it?

M10 resin anchors or thunderbolts.