Flat roof dilemma

[pritch]

I've been chatting to a builder who reckons if I stop the joists at the wall plate instead of carrying them through to the brick they will look better because I won't need a big soffit and facia board.  

I quite liked the idea of an over hang  for installing spot lights.  

I'm not sure which to go for ? 

Can anyone give me any advice? 

Thanks 

Edited May 30, 2019 by pritch

[ToughButterCup]

11 minutes ago, pritch said:

[...]

if I stop the joists at the wall plate instead of carrying them through to the brick they will look better because I won't need a big soffit and facia board.  I quite liked the idea of an over hang  for installing spot lights.  

[...]

 

Traditionally, the person paying the piper chooses the tune.

[PeterW]

Overhang looks much better on a flat roof like that, but I would want to put hidden gutters in and make the fascia nice and tidy. Which way does the "flat" roof slope..?

[lizzie]

@pritch I have overhangs on East and West elevations and lights in them.  Works well, gives a bit of shading from sun too (could do with a bit more really).  On our North and South elevations we did not do overhangs because they were unnecessary and a bit impractical.... they are at the side and back of the house so we dont see them anyway.  We used low level lighting there instead. I have hidden gutter and only two downpipes on whole house.

[Russell griffiths]

You need the over hang,  facia finishing level with wall looks crap imho, what you do is reduce the depth of the joist after it has rested on the wall plate, so the non load bearing part gets reduced in depth, then build up another course of bricks to allow a slimmer more elegant facia

some of these new builds with there deep rafter depth and high roof trims end up looking like a supermarket. 

[Mr Punter]

You could have the joists a bit shorter and screw some smaller section timber to the sides for the overhang.

[Jeremy Harris]

Just now, Mr Punter said:

You could have the joists a bit shorter and screw some smaller section timber to the sides for the overhang.

 

 

This is how our pitched roof has been done, using ladder frames all around to create the overhangs at the eaves as well as the barge boards.  The reason for it being down this way for us was to reduce the thickness of the overhangs, as our rafters are just over 400mm deep, so if they had been allowed to overhang we'd have had to cut them back in order to get a reasonable look.

[pritch]

4 hours ago, PeterW said:

Overhang looks much better on a flat roof like that, but I would want to put hidden gutters in and make the fascia nice and tidy. Which way does the "flat" roof slope..?

Hi

I haven't really thought about that yet.  The rsj only goes on next week.  

Do you usually have the one hidden gutter at the front? 

Thanks 

[PeterW]

Yes but how big is this room as it will affect the slope / firrings required to get a 1:80 fall on it.  

 

For me, I would stop the large joists at the inside wallplate then continue them as per what @Mr Punter has suggested with say a 150x50 for a decent overhang but drop them to 50mm below the top of the main joists. Then use a 200x50 on the front as a fascia   carrier and you’ve created a hidden gutter of 50mm deep across the full width of the front that is only 200mm high. This gutter can be built up so it slopes both ways from the centre and a downpipe at either end. 

 

That would mean your slope is from the house to the front - what are you using for the waterproof layer..?  GRP or something else ..?

[Conor]

I'm in a similar position, currently have it designed as a parapet roof. Much prefer the skinny, long overhang long. Thinking of building the roof as normal to the top of the wall level. Instead of going on up with perimeter wall etc, I'm thinking of building on another timber structure on top of the whole lot. This would sit on top of both the top of the walls and the roof deck. Extend out using 100mm joists, tapering to maybe 50mm at the end. Would then be covered in OSB and the waterproof coating (GRP). Drip notches, flashing etc TBC!

[lizzie]

7 minutes ago, Conor said:

I'm in a similar position, currently have it designed as a parapet roof. Much prefer the skinny, long overhang long. Thinking of building the roof as normal to the top of the wall level. Instead of going on up with perimeter wall etc, I'm thinking of building on another timber structure on top of the whole lot. This would sit on top of both the top of the walls and the roof deck. Extend out using 100mm joists, tapering to maybe 50mm at the end. Would then be covered in OSB and the waterproof coating (GRP). Drip notches, flashing etc TBC!

Mine is that ...its a separate cold roof structure on top of the flat warm roof. Covered in single ply membrane.  Our top roof is not a tually flat it is shaped like lopsided butterfly higher one side than the other with a flat section in the middle where the hidden gutter runs, everything falls into the middle. We had special tapering timbers made to form the shape.  Our large fascias are because of the shape of the roof and our overhangs were dictated by the engineering for our very exposed location, didn't want it lifting and blowing off.

[pritch]

4 hours ago, PeterW said:

Yes but how big is this room as it will affect the slope / firrings required to get a 1:80 fall on it.  

 

For me, I would stop the large joists at the inside wallplate then continue them as per what @Mr Punter has suggested with say a 150x50 for a decent overhang but drop them to 50mm below the top of the main joists. Then use a 200x50 on the front as a fascia   carrier and you’ve created a hidden gutter of 50mm deep across the full width of the front that is only 200mm high. This gutter can be built up so it slopes both ways from the centre and a downpipe at either end. 

 

That would mean your slope is from the house to the front - what are you using for the waterproof layer..?  GRP or something else ..?

Yes grp.

I think I understand what you mean but I'm not really familiar with flat roofs. 

Here are the drawings. 

I'm sure we're ok to tweak these without  a problem. 

Thanks 

[Ferdinand]

One one of mine the joists simply continue through the wall and form a 1m overhang, which I really like - but which might have thermal-break issues in 2019 which were not perceived in 1970.

 

It was a flat roof but now has cathedral ceilings and joists crossing at the former ceiling height - really attractive.

 

For roof overhangs I really don't like the idea of building outriggers or extensions because the rafters are in some way unsuitable. It is what it is and we don't imo really want to add a pastiche overhang. It makes me think of those grand designs which have attempted to recreate Mies van der Rohe by design bodgery rather than doing it a la Mies.

 

I would find the idea of longer rafters with the corners cut back on a diagonal to be more attractive.

 

(No - I have no idea how I would solve this for a flat roof in 2019. I would need to think of something.)

 

On "solar sheltering" overhands - yes but make sure they are big enough. Mine mentioned above was done to provide relief from Southern Sun, and at 1m approx 2.7m off the ground it is a little too short.

 

Best of luck, all.

 

Ferdinand
 

[mvincentd]

I used 4" x 3" timber sliced to make furrings. Where they reduce to near zero is the unseen back of my house so the roof deck just rolls into standard gutter.  At the front I have the benefit of the chunky 4 x 3" atop the joists.  I stopped the joists at the inner leaf but continued the furrings to create a small overhang and brought the deck to the furrings edge.  I fixed upward through furring and deck into 8" x 2" to make a perimeter to the deck (I needed the 8" height to contain green roof materials).  This and the furrings provided ample structure to create a batoned base for my horizontal cedar fascia.  The outer leaf was built up (almost) to underside of furring and the facia overlaps by hanging lower.  If it's a warm roof plan early for airtightness, perhaps using a 'tony tray' that envelopes the furring extensions.

This approach only worked though thanks to my only needing overhang at the fat end of the furrings...so it's limited.

[pritch]

On 30/05/2019 at 17:03, PeterW said:

Yes but how big is this room as it will affect the slope / firrings required to get a 1:80 fall on it.  

 

For me, I would stop the large joists at the inside wallplate then continue them as per what @Mr Punter has suggested with say a 150x50 for a decent overhang but drop them to 50mm below the top of the main joists. Then use a 200x50 on the front as a fascia   carrier and you’ve created a hidden gutter of 50mm deep across the full width of the front that is only 200mm high. This gutter can be built up so it slopes both ways from the centre and a downpipe at either end. 

 

That would mean your slope is from the house to the front - what are you using for the waterproof layer..?  GRP or something else ..?

I like the idea of this but not sure how it would work in with the warm roof design .....120mm insulation ,19mm ply board?

I'm struggling to actually find someone to do it.  I can get your average chippy and roofers but but not someone experienced with these flat roof designs.  

[nod]

An over hang looks really slick on a contemporary look 

we decided to sit the joists on the inner leaf and cap with copings 

 

[nod]

 

[laurenco]

On 01/06/2019 at 09:31, nod said:

An over hang looks really slick on a contemporary look 

we decided to sit the joists on the inner leaf and cap with copings 

 

 

Nothing to do with the roof.. this floor is amazing. Is it real wood? laminate? tile?

[nod]

1 hour ago, laurenco said:

 

Nothing to do with the roof.. this floor is amazing. Is it real wood? laminate? tile?

?wish I had a pound each time I hear that 

 

no I laid Italian Porcelain 1200 x 200 planks 

150 square mtrs downstairs 

 

[scottishjohn]

yes.

porcelain  tile planks is what i will be going for 

looks like wood ,but none of the problems 

would never go back to a soft floor after having hard ones for 10 years .

 

[nod]

1 hour ago, scottishjohn said:

yes.

porcelain  tile planks is what i will be going for 

looks like wood ,but none of the problems 

would never go back to a soft floor after having hard ones for 10 years .

 

Exactly John 

The Italian Porcelain doesn’t chip or scratch either 

[pritch]

Hi

I've got marine ply 19mm on the drawing but it's double the price of osb board.  

I take it osb will be sufficient? 

Thanks 

[Conor]

8 minutes ago, pritch said:

Hi

I've got marine ply 19mm on the drawing but it's double the price of osb board.  

I take it osb will be sufficient? 

Thanks 

Yes. OSB 3 is perfect for the job. It should be covered by your roofing membrane on the tops and edges, underside should be ventilated.

[pritch]

So how many of you did your own flat roof..just the timber part? 

I'm being quoted some crazy prices by chancers who think you have deep pockets because you live in a nice house.  

I'm very much hands on but I thought I'd leave this to the experts. 

I'm now seriously thinking of having a go myself.  

Edited June 6, 2019 by pritch

[lizzie]

my carpenter did mine