Dormer

[slimj]

Hi all,

I have stripped out my attic room internally and I exposed the dormer. There have been signs of leaking in here for a while but I wanted to see where it was coming from.

Anyway, after removing everything I can see the dormer as been leaking a fair bit; this seems to be concentrated on the roof deck and is really a separate issue to my query. Certainly the rafters all look sound which is good news.

My query is that looking at the dormer construction I don't think the ridge header (3x2) is beefy enough. The existing rafters (also 3x2) have been cut and nailed to it and with the dormer (additional water or not) it will be carrying a lot of weight and it is clearly bowing at the moment...

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Also, I thought that when dormers are constructed it was good practice to double up on the rafter directly to the side of the dormer? In this case that also hasn't been done.

Please can someone advise what remedial actions I should take? Swap the ridge header? Double up the rafter? The less work the better obviously but it needs doing properly.

Thanks.

 

[ree]

Can you post pics showing the outside of the dormer, & detailed interior close-ups? Your pics are blurred.

From what i can make out, the piece you refer to as a ridge header is actually a lintel beam that is also a header. Its too difficult to clearly see how its connected for support, & if its adequate in section, or even if its doubled.

Yes, the side common rafters should be doubled. The header should be doubled and any lower plate should be doubled.

When the roof is stripped for renewal you could remedy any rafter framing details. google pics for shed roof dormers.

 

[slimj]

Thanks ree.

Yes, I can certainly make any amendments I need to when I re-roof. Just i need to start planning and buying what I need now.

I will post a load more photos later. I had just stripped the lath and plaster so there was lot of dust in there yesterday - taking pictures was a challenge.

 

[slimj]

Rather than just take some images, I have sketched out the current setup.

The dormer timbers (shown in yellow) are not complete. The dormer roof is but the side supports and the front setup isn't shown.

I have coloured the different timbers to hopefully show in better detail someone's handy-work!

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I have also taken a bunch more images in the hope someone can give me a breakdown on what to do to get it right and get it safe.

Many thanks all.

slim_j


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[ree]

The upper header is failing.
A tremendous amount of load is on the two trimming common rafters.
Two posts are also taking weight from the trimming rafters - what are the posts standing on or fixed to?
The purlin - does it run from a masonry wall to a masonry wall?
Is the purlin being supported/propped in the centre of its span?
One of the pics appears to show the ridge area with what looks like fungal damage?

I understand that the dormer roof is to be replaced - but is the main slate roof also going to be re-fixed to modern standards? Keep your slate, & on no account replace with conc tiles.

What is required here OP is a professional on site view from a builder. This is not a DIY job.

I suspect, given the carpentry framing in the pics, that the loft floor might also need investigating - just a hunch.

I should replace the dormer roof with a pitched roof.

 

[slimj]

The upper header is failing.
A tremendous amount of load is on the two trimming common rafters.

Agreed!

Two posts are also taking weight from the trimming rafters - what are the posts standing on or fixed to?

A bottom plate fixed to the floor deck.

The purlin - does it run from a masonry wall to a masonry wall?

Yes.

Is the purlin being supported/propped in the centre of its span?

I do not think it is, but I will inspect more.

One of the pics appears to show the ridge area with what looks like fungal damage?

There is some fungal damage from some water ingress over a long period of time.

I understand that the dormer roof is to be replaced - but is the main slate roof also going to be re-fixed to modern standards? Keep your slate, & on no account replace with conc tiles.

Looking at the construction in more detail, I will be rebuilding most of the dormer. I am a DIY'y and without any planning can do substantially better than this.

I am also going to re-roof but I will definitely not be adding any additional loads associated with concrete tiles. Slates relay only.

As a separate question, when I remove the slates should I clean or prepare them in any way prior to relaying?


Once I have stripped everything off, I am still keen to take it on.

Stage 1 will be to double or triple up the rafters to either side. I will widen the dormer slightly so that is is not finishing mid-way between the rafters as before. (The more I think about the design of the old dormer, I think it must have been built around the window. Presumably the owner had a uPVC window knocking about and wanted to fit it in somewhere!)

Anyway, the header will also be renewed and doubled up...

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Once complete the dormer can be rebuilt. The roof timbers and wall studs for the dormer might be salvageable but the rest will probably be scrapped.

A new plate can be fixed over the rafters and new studs fixed to that. The lower header can then be renewed and doubled up and some supports inserted for the bottom header and purlin...

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I suspect, given the carpentry framing in the pics, that the loft floor might also need investigating - just a hunch.

You might be right on this. Certainly the room has been used as a bedroom for a long time without any issue but that certainly doesn't mean it was installed and checked correctly.


I really welcome any advice on this from joiners or engineers. The roof is 35 degrees and the rafter span is about 5.3m. The width from party wall to party wall is about 4.2m.

Cheers, slim_j