Dormer and load distribution

[cederbusch]

I know that this is frequently asked about on BH, but it's hard to find the answer for my specific situation, so I'll make a thread.

In our house, we have three adjoining rooms on the upper floor, see the picture. The picture isn't completely accurate but gives a general idea. The middle room mainly extends into the old attic space and feels cramped.

We've talked about installing one or two skylights but are now considering a dormer. It would be in the same style as the one at the front, but smaller. It's also not possible to build the dormer centered with the other one, so it will be offset.

I'm handy and would like to build it myself but feel a bit uncertain about the support system. The rafters are placed just under a meter apart, so removing a rafter would be relevant. I've read that reinforcing the two adjacent rafters might be enough, but maybe that applies to 60cc? Mine are fairly sturdy.

It feels like it shouldn't be that complicated to manage. Or is it better to hire a carpenter to build the frame and then I can complete the rest? An alternative might be to settle for a dormer between two rafters, but it would be nice to have more floor space.

 

[Matti_75]

It is usually enough to prop up the truss and saw it off. Then you place a brace between the two adjacent trusses with joist hangers to attach the cut one.

 

[cederbusch]

Thank you Matti! Maybe a silly question, but why not set the rule first and then just saw? Or have I misunderstood what you mean by stamping?

I notice I'm asking the same questions I've read many of here, but it's hard to find the answers. Are there any standard drawings available to download for examples of dormer construction with a straight, sloping roof? What are the critical aspects of a dormer (flashing, rule dimension, transitioning)? And what could a simple dormer of maybe 2 meters cost in materials?

I understand that it's best to bring in an engineer to tell me what to do (might have to have drawings for the municipality anyway), but I think it should be possible without that.

 

[Matti_75]

Thank you Matti! A silly question perhaps, but why not set the rule first and then just saw? Or have I misunderstood what you mean by stamping?.

You must stamp up the truss so that it does not sink when you cut it off. The critical part in the dormer construction is to get the connection of the new roof to the old one. It only requires common sense when you're building a dormer.

 

[Sommartorparn]

We have talked about installing one or two skylights but have now started considering a dormer. It would be in the same style as the one at the front, but smaller. It is also not possible to build the dormer in the center of the other, so it will be offset.

Hmmm, will it look good?:S

 

[cederbusch]

You need to prop up the roof truss so it won't sink when you cut it off. The critical part of dormer construction is connecting the new roof to the old one. It only requires common sense when building a dormer.

What exactly do you mean by "stämpla"? I understand it as setting props like when demolishing a wall that needs support. Then you remove the props. Do you mean that in this case the prop should remain in place?

I'm considering the alternative of installing two skylights side by side instead of a dormer. Then I would also remove a roof truss, or possibly split it in the middle so it doesn't take up as much space and support it in another way. Or would that result in too weak a construction? The weight of the snow that lands at the level of the windows wouldn't be supported anywhere then.

 

[Matti_75]

I mean stämpa. You remove the stämp when you have finished switching the truss as I described in my first post. A beam across between the adjacent trusses that supports the cut truss.

 

[cederbusch]

Now the penny dropped! I kept thinking that I would place two beams, from side to side so to speak, but now I realize that the new beam should be attached to the cut created when the chair is sawn off. Sometimes you're unlucky to think the wrong way.

Any tips on where I can find suitable dimensions and construction methods?