How to construct a roof for a conservatory with a small slope?

[YNWA67]

Hello!
I'm planning to build a sunroom adjacent to the living room.
6m wide and 6m deep.
The roof structure can be a maximum of 40cm high with an outward slope of 2cm/m.
I don't want any posts inside the room, but I can have one in the middle along the outer sides.
I’m considering sheet metal on the top.
My question; would some kind of steel beam as joists be an alternative to laminated beams since I want to maximize the ceiling height?

 

[fb35523]

The slope is on the small side. What kind of roof are you planning, polycarbonate sheets? I used regular 45x210 beams but I have just under 5 meters from the inner wall to the outer wall. They like to sell expensive glulam beams, but good beams that are painted shouldn't twist. I have 40 mm Willab polycarbonate sheets. Steel beams aren't as easy to fasten as wood, but it's really no problem. I find it hard to believe that you wouldn't be able to fit in a glulam beam and a roof at 40 cm. On the other hand, maybe 40 cm must also include the slope in your case, right?

 

[justusandersson]

A length of 6 meters for the roof beams is not possible without glulam or steel. Assuming the house is in snow zone 2, either a 90x270 glulam or HEA 120 steel is required, in both cases at c/c 600 mm. The glulam costs about 16000 kr, and the steel about 33000 kr.

 

[YNWA67]

The slope is quite small. What kind of roof are you planning, polycarbonate? I used a regular 45x210 beam, but I only have just under 5 meters from inner wall to outer wall. They like to sell expensive laminated beams, but good beams that are painted shouldn't twist. I have 40 mm Willab polycarbonate. Steel beams aren't as easy to attach as wood, but they aren't really a problem. I find it hard to believe you couldn't fit a laminated beam and roof in 40 cm. On the other hand, maybe the 40 cm has to include the slope in your case, or?

I'm thinking spontaneously of a roof covered with banded metal. Yes, the 40 cm must include the slope of 6m x 2cm = 12cm. So remaining for the roof construction is then 28cm.

 

[YNWA67]

6 meters length of the roof beams is not possible without glulam or steel. Assuming the house is in snow zone 2, either glulam 90x270 or steel HEA 120 is required, in both cases at c/c 600 mm. The glulam costs about 16000 kr, the steel about 33000 kr.

Thank you very much, then I have something to calculate on. Glulam should actually fit then.

 

[largab]

https://www.byggbeskrivningar.se/dimensionering/med-meny/

 

[YNWA67]

[link]

Thanks. Hmm. It says 90x405 and yet it's showing red. Probably need to consult a constructor who can calculate it anyway.

 

[justusandersson]

You must have entered the wrong values. The answer is obviously unreasonable. A 90x405 mm 6 meter long glued laminated beam can handle an instantaneous load of about 800 kg per meter without bending down more than the span/300. One should have good knowledge of structural engineering to use that type of calculation app.

 

[YNWA67]

Then you must have entered incorrect values. The answer is obviously unreasonable. A 90x405 mm 6-meter-long glulam beam can handle an instantaneous load of about 800 kg per meter without deflecting more than span/300. Good knowledge in structural engineering is necessary if using that type of calculation tool.

Thanks, you're absolutely right, I will take my drawing to a designer, who will size it up.

 

[Rickard.]

One thing that might be worth looking at is that 2cm/m is just over 1° and the minimum recommended slope for double-seamed sheet metal is about 6°.

Now, I don't think it's super important to achieve the recommended slope on such a simple roof, but it might be worth getting a little more margin.

 

[fb35523]

I also noticed the slope, but I have kanalplast and that's something completely different. I didn't have the confidence to say what Justus said, that it sounded quite extreme with 90x410. I have 45x210 over approximately 5 meters (don't remember the exact measurements) and that's with a regular C24 beam. It's not recommended by Willab because, unlike a glued laminated beam, it runs the risk of bending, but the strength should be OK (snow zone 1 or maybe 2, Halland).

 

[p-pennan]

We built a conservatory last winter with a slight slope and without middle posts. I solved it by having "whole" corners with about 60cm walls. The construction becomes sturdier and the sagging much less. Ended up with a little more than 1 degree but just above the limit for what a felt roof is okay for. Made a thread about it with pictures so you can see how I solved it. Used laminated wood straight across all the beams.

 

[YNWA67]

We built a conservatory last winter with a slight slope and without center posts. I solved it by having "whole" corners with about 60cm walls. The construction becomes sturdier and deflection is much less. However, I ended up with a little more than 1 degree but just above the limit for what's acceptable for a felt roof. I made a thread about it with pictures, so you can see how I solved it. Used glulam beams straight across all the beams.

Saw your pictures. Nice solution

 

[YNWA67]

I also reacted to the slope, but I have channel plastic and that is something completely different. I didn't have the confidence to say what Justus said, that it sounded too extreme with 90x410. I have 45x210 at about 5 meters (don't remember exact measurements) and that with a regular C24 beam. It is not recommended by Willab because it, unlike a laminated beam, runs some risk of bending, but the strength should be OK (snow zone 1 or maybe 2, Halland).

Thanks. What I'm unsure about is when I should have raw planks + banded metal roof, how it affects the weights.
So it will have to be a constructor for this.

 

[justusandersson]

Tongue-and-groove boards plus seam roofing with sheet metal is a very lightweight roof construction. Generally, the largest roof loads occur due to snow load.