Garden Room - Flat Roof Design

[^woody^]

Ok, ignore the gutter lovers and parapet haters, here we go.

In this case, I fitted the brackets below the gutter. There was a timber backing board fixed before the plastic fascia which went up past the gutter.

 

[Leofric]

Nor do they have a catastrophic negative aesthetic effect either. If you are busy gawping at the lack of beauty and architectural splendour of your gutter, then you need get a hobby.

this is all becoming weird.

 

[Leofric]

In this case, I fitted the brackets below the gutter. There was a timber backing board fixed before the plastic fascia which went up past the gutter.

that's definitely a gutter hater's detail

 

[efunc]

So, I’m back with a brief progress report and a question regarding fascias, trims and soffits. So as you can see, the frame is now mainly up and the roof has been decked. The rafters are 150mm high and the front overhang extends 600mm out. Today we cut a recessed ‘channel' through the roof deck at the front (about 40mm back from the edge) which will be re-lined with more OSB3 and then covered in GRP with the rest of the roof deck. This will form a concealed box gutter which will fall towards a hopper out to the left-hand side:

We will use GRP Drip trim on the front, Raised Edge Trims on either side, and Wall Fillet at the back. We were going to do the fascia in OSB3 and then clad in T&G Larchwood cladding like the rest of the building, however for speed and neatness I’m just looking into Aluminium or uPVC fascias and soffits. I have no experience of these so had some quick questions:

Firstly, are these uPVC fascia boards simply pinned directly to the rafter ends, or should we still do OSB over the front rafters and then glue/pin the uPVC fascia board onto that? The width of the roof is 6m, so I would need a 5m board and then an extra meter with an in-line joiner. If I put this directly onto the ends of the rafters does it have adequate strength to hold its form over 5m? Also, am I right in thinking 175mm would be the correct fascia height to accommodate the rafter and the soffit underneath?

Likewise for the soffits. I was going to do this in OSB with larch wood cladding, however I’m thinking of prefab uPVC soffit board. Since the overhang is 600mm you don’t normally see soffit boards in this width, but I presume two 30mm T&G boards would be what I’m after? Also, since I need to secure 4 LED down lights in the overhang and I OK to do that or will the strength of these boards be much less than the OSB option?

 

[efunc]

OK, I've figured out that the 10mm Fascias are designed to go over existing OSB, but the 18mm ones would attach directly to the rafter ends and forego the need to fit OSB. What about the soffits? Can I do the same and find 18mm soffit boards which would allow me to install vents and LED downlights directly in them with no need for OSB boarding? Is one approach better than the other?

 

[^woody^]

The furrings don't appear to be actual furrings. Why are they so thick at the ends?

 

[efunc]

Those are not the actual firrings. My original build used 4x2 timber, so when I dismantled it I re-used many of these for the roof rafters but got additional 2x2s and bonded and nailed them to the 4x2s to make up stronger beams. It's a compromise but seems to do the job perfectly fine. The firrings are 60mm at the back but tapered out at the front so you can't really see them.

 

[efunc]

Concealed gutter well on its way, and working quite well now that the weather's turned wet. I could have put it further to the edge, but there's not much in it:

I'm not bothering with uPVC fascia board as the GRP edge trim is actually itself quite deep:

What remains is to connect the rainwater outlet to a water butt situated against the rear brick wall to the left of the structure. The problem is there is no rainwater so it'll be receiving the entire volume of rainwater into a butt (rather than diverting to it from a drain pipe). I guess I'll just be letting it overflow when the 210L butt is full. Do they have some sort of valve to allow them to spill out the top of the butt, or will the water eventually be backed up all the way to the roof?? I could presumably put a diverter valve at the top of the butt and have the overflow runoff into the lawn.

2nd question: I will place a soffit vent strip in the overhang, but does there need to be air inlet at the back of the roof at all? Obviously mine's a lean-to, so that's not really in the design. I could think about put a screened vent on the rear corner though. It's not much, but it could be something..