The Carport.

[ProDave]

A part of my build that is still awaiting to be built.

 

And a good job as the parameters have changed as I hinted in another thread a few days ago.

 

It now needs to be built a bit higher than originally planned to accommodate the latest addition to the fleet.

 

 

It's almost 3.2 metres to the highest point so we need comfortable clearance under for that.

 

The size remains the same, 6 metres by 6 metres.  The original plan would have been sloping down from the front to the back, but that would make the front insanely high now, so it will now slope from the garage wall down towards the left.

 

It will be roofed with box profile roofing as originally planned.

 

I will sketch a proposed joist plan in due course to bounce ideas around.

 

But one thing that has become obvious, the car port roof where it attaches to the garage is going to be above the MVHR vents.  I am not sure if that is going to pose a problem or not?

[Iceverge]

I would be worried about some future owner running a car in there on a cold morning to warm it up and the fumes getting drawn into the MVHR. 

 

Could a stand alone structure work?  Or you could always extend the MVHR inlets  out to the fresh air above the new roof . 

[ProDave]

I could extend them (externally) one to the front and one to the back so they were not actually under the canopy.

 

The front one visible is the exhaust, the rear one, hidden in this picture is symetrical so the same distance is the inlet.

 

There will be a small gap anyway, to avoid trying to form any sort if flashing from the wall to the roof.

[Russell griffiths]

You will need next to sod all fall if using box profile sheets. 

[Oz07]

Just been in Australia and nowadays for their patios they are using all these insulated roofing sheets. They seem to be able to get massive spans without intermediate joists or purlins. Possibly worth looking into very simple construction. Saying that you do get big snow loading presumably so prob a no go

[JohnMo]

Stick big 500W plus solar panels on the roof? 

[ProDave]

31 minutes ago, JohnMo said:

Stick big 500W plus solar panels on the roof? 

That is the plan, with battery storage as well.

[Russdl]

How about a freestanding carport, half a meter or so away from the house so the MVHR isn't affected. Park the truck the other way round and have a slight fall front to back.

[ProDave]

42 minutes ago, Russdl said:

How about a freestanding carport, half a meter or so away from the house so the MVHR isn't affected. Park the truck the other way round and have a slight fall front to back.

There will likely be a gap but it can't / won't be that much, the supporting poles will be attached to the garage wall for stability.

 

The whole point of buying this particular type of truck is you can wind he legs down and demount the camper unit from the truck, and use the truck on it's own as a normal vehicle.  So parking the other way would mean driving out onto the grass to demount which would not end well in winter when it is wet and soggy.

[ProDave]

First stab at joist plan for the car port roof

 

There will be 6 posts "P" 3 each side, probably 150mm square all supported on post feet. The 3 at the garage ends will also be bracketed to the wall, to locate them, not to take any weight on the garage wall.  The 3 at the left hand free standing end will require some diagonal bracing.

 

Box profile roofing from the garage high end to the free low end.  Probably with a small gap at the garage end to avoid having to flash it to the wall.

 

Total size 6M by 6M.

 

Box profile roof needs supporting on joists running across it, so in this case front to back joists.  Assumed at the moment 600mm centre to centre spacing  they are Joists B in this plan and each need to span 3 metres.  I don't think these are going to be difficult.

 

The problem ones I think will be the 4 "Joists A" that have to span 6 metres and support the smaller joists.  This is the one I need some design input to see if this proposal is viable.  I would rather they were not too deep, say no more than 8" / 200mm.  But I do expect to double or even tripple these, and there is the possibility of a steel plate between them to make it a flitch beam?

 

Ideas please?

 

 

[Iceverge]

Box profile only needs to supported every 1200mm so I don't think you need anywhere near as many "joist B".

 

The 6m span is the tricky part and all the timber going the other direction isn't doing a tremendous amount really. I'm not sure Filch beams are worth the complexity. Steel would prob be easier at that rate. On both these counts I don't like having timber interfacing with steel in an unheated environment ,if it's avoidable, as the condensation that the steel attracts will rot the timber eventually. 

 

 

Finger in the air, farmer "engineering" here...... I'll try to avoid anything bigger than 225*75 as it doubles the price very quickly.

 

 

I would erect 5 x 150*150 posts at 1500mm centres along the low and high side of the carport. Notch the tops of the posts and drop in a single 225*75mm timber running the full length of the carport as an end support beam. Add appropriate diagonal bracing on the low side to stop it wobbling. 

 

Drop 9x 225*75mm rafters on top at 750mm centres and secure them to the end beams with metal straps. Add 225*44mm noggins at 1200mm centres to take the fixings for the metal roofing. 

 

I would put a roofing membrane under the metal roofing too to stop it dripping in winter. 

 

Edited November 17 by Iceverge

[saveasteading]

It's a car port. If it looks OK it is OK.

I'm not doing any calculations , but suggest doubling up the big ones, bolted together. Ie 2 instead of 1.

Once it's built, if it feels OK, that's it, if it doesn't, ask again.

 

Failure would be from snow load, drifting against the wall, so clear it, or stay out.

 

Def diagonals at the beam to post junctions for stiffness. Will look better too.

[ProDave]

Interesting ideas @Iceverge

 

So you are suggesting a 225 by 75 would span 6M if it was not carrying too much load? and suggesting 5 of them.  My design already has 4 of them so not that different.  I would rather not go as many as 5 posts each end perhaps compromise on 4.  I will have to mark it out on the ground to see how it would look in reality and where they would land.

 

Yes I thought the box profile could get away with fewer cross beams.

 

I don't want to stack the cross beams on top of the long beams, that adds to the height which is also very high, I want to drop them between the long beams on joist hangers.

[ProDave]

6 minutes ago, saveasteading said:

It's a car port. If it looks OK it is OK.

I'm not doing any calculations , but suggest doubling up the big ones, bolted together. Ie 2 instead of 1.

Once it's built, if it feels OK, that's it, if it doesn't, ask again.

Yes the crux is definitely the long beams, how many and what size.  I guess I need to phone a timber merchant and get some prices and work out the best bang for the buck from what is readily available.

 

I will still ask my neighbour (who works for a steel company) about steel plates to make a filch beam.  For a laugh I asked him to estimate for doing a steel frame for the whole lot and his answer was "do it in timber"

[Iceverge]

2 minutes ago, ProDave said:

So you are suggesting a 225 by 75 would span 6M if it was not carrying too much load? and suggesting 5 of them

 

Yes but I was being a bit more conservative and suggesting 9. It worked out nicely so that each rafters was falling half way between or on a post too. Honestly, I think I'd need to draw it accurately so I could mentally "jump" on it to see if it looked ok!

 

 

 

 

 

 

 

 

[Iceverge]

My frame of reference for this is a loft we build in a shed on the farm.

 

It's about 6m span with 9*3 sawn timbers @450mm cc. These are full fat, hairy, skin on timbers cut on the farm so there's a good bit more to them than a regularised commercial timber. 

 

None the less they hold , at a guess, about 4tonnes of material although it is mostly more long timber planks so the load is probably partially carried by the planks themselves. I'm not sure if put 4 tonnes of sand up there. 

[dpmiller]

what about cold rolled steel sections rather than timber?

[saveasteading]

6 hours ago, ProDave said:

his answer was "do it in timber"

Up your way there is no shortage of timber, and getting deep beams shouldn't be difficult. So 9" or 10" would be an easy improvement over 8". The improvement in strength being approximately based on  the square  10/ 8  to  100/64 ie very much stronger.

BUT your local timber is mostly C16, so find C24.

[Iceverge]

If it gets too thick it'll take the cab off his jalopy though!

 

Here's a question for the engineers. @Gus Potter @saveasteading and anyone else I forgot. 

 

We regularly scissor timbers beside eachother for more strength. 

Why don't we make "I" beams? 

 

Wouldn't this be a far stronger arrangement of three 175*44 timbers say than 3 of them scissored together? 

 

Sure it would take some glue and screws but why wouldn't it work?

Edited November 18 by Iceverge

[ProDave]

We demounted the camper from the truck this morning.  This is why we chose this type of camper, when not off camping, it becomes a perfectly normal truck for other uses.

 

 

It has been lowered on it's legs just now, but the car port still needs to have enough clearance for it to go under it when on the truck.

[saveasteading]

13 hours ago, Iceverge said:

Why don't we make "I" beams? 

Simply the work involved. 

Commercially they are made with osb as a Web, in a very fancy production line:  see John James video.

Diy would need an SE spec and precision work, so it's easier and cheaper to have excess wood in the central area.

OR make a box beam with timbers top and bottom and ply sides....again it needs calculation and isn't  worth it for a small job.

[Iceverge]

58 minutes ago, saveasteading said:

Simply the work involved. 

Commercially they are made with osb as a Web, in a very fancy production line:  see John James video.

Diy would need an SE spec and precision work, so it's easier and cheaper to have excess wood in the central area.

OR make a box beam with timbers top and bottom and ply sides....again it needs calculation and isn't  worth it for a small job.

 

 

But...................

 

If someone was say, building a timber carport..........

 

With some glue you could bang one together in 5 mins. No routing or anything fancy. 

 

No ripping of ply. Is it an issue of making sure the horizontal "flanges" stay horizontal?

 

I might make one if I have a few "two bys" hanging about 

Edited November 18 by Iceverge

[Gone West]

1 hour ago, saveasteading said:

Commercially they are made with osb as a Web

Some use OSB others such as Steico use structural fibreboard.

 

STEICOjoist and STEICOwall are natural products.
The production basis for all our joists is timber. Made from slow grown
spruce, the flanges are kiln dried and machine stress graded thereby
guaranteeing a consistant quality and defined mechanical properties.
The webs are made from structural fibreboard, jointed along the length
with a V-groove profile, offering a very high shear capacity. Both the
preparation and manufacturing processes of the flanges, the webs and
the installation of durable adhesives are carried out using the latest
automated assembly lines.

[Gus Potter]

On 18/11/2024 at 00:30, Iceverge said:

Here's a question for the engineers.

Hope this helps a bit.. but when we want to create a void above the wall head level the forces in the roof members change a lot . The following is very simplistic but intended to give folks an insight into some of the things we design for and hopefully give you all some ideas.

 

Below is a standard fink truss.

This fink truss is triagulated, very economic an importantly the loads at the supports are downwards.. and upwards when you get wind uplift. A lot of roofs can be "uplifted"..

 

Below is what we call a raised tie truss.

 

 

Here we have an extended leg. The ceiling tie and wall support create a lever arm... like having a long spanner to take off a wheel nut on your car. This type of truss depending on the length between the ceiling tie and the wall support causes other forces / sideways movement which can grow exponentially with a small increase in length. An important one is that this kind of truss can push the wall outwards (sideways movement).. so you often need to have "special" sliding truss clips at the wall head or a very strong wall.. and if you have a very strong wall then there are other options!

 

Now the above truss generates some nasty forces at the connection between the ceiling tie and the sloping rafter. Timber connections can be quite weak and they are hard to design economically / buildability wise once you reach a tipping point.. which can be quite early on.. this can be a hard lesson for a Graduate Engineer / self builder.

 

Below is a scissor truss

 

 

Here you can see that the sloping ceiling tie stops the forces that want to spread the walls outwards as the bottom of the scissor is conneceted to the wall head.

 

Often when we design timber roofs one of the problems is not the size of the timber but having enough timber to make the connections work ok.

 

If you have an old house with a traditionally cut roof you'll see that the ceiling ties and soldiers (the short upright bits) are 1/3 to 1/4  checked. Below is a screenshot of one of my drawings that shows this.

 

The dark green bit is the rafter, light green the soldier/ ceiling tie framing in. But there are only three nails! The one shown here is later detailed as having only 3 no 90x 3.1 mm dia Passlode ring shank galv nails.

 

The three nails are there just to hold the soldier in place when there is say snow / access and roof self weight on the roof. The check in the timber allows for direct bearing.. timber to timber contact... much "stronger" than a few nails! Also we need to watch out for nail spacing and edge distance.. to many nails / to close to the timber edge and we weaken the timber so folks bear that in mind.

 

The three nails are enough to hold the connection together when the wind is trying to suck the roof outwards.

 

To sum up. Timber roof design is a bit of an art.. but hope the above gives some insight into what it is all about. The key thing is that often its the connections that govern the design rather than raw timber size. A good starting point is to go into some old buildings/ terraced houses and see how the roof is put together.

 

@ProDave If you want to chew the fat then would be delighted to hear from you, mind you I'll want to pick your brains too so no free lunch!