Single storey extension

Chameleon · 19 Aug 2011

I'm building a single storey in my garden which will be 14' wide x 12' deep and with a max room height of 2.5m. It's exempt from building regs and planning, but I need some advice regarding the roof. I'm planning on a hip roof, which will be tiled. With a max height of 2.5m will I have an adequate pitch or will I need to reduce the wall height?

It will be constructed of brick and block and will be used as a studio, so I'm flexible in terms of the final design.

Also where can I go for advice on trusses and general roofing materials required?

Richard C · 19 Aug 2011

If the maximum room height is 2.5m I puzzled how the max tiled hip roof height can also be 2.5m!

I’m not a roofer & haven’t calculated in detail but to get an internal wall height of, say 2.1m, I think you will need to go down to 15 degrees or even less. You need a minimum angle of 22.5 degrees for standard roof tiles & even with specialist tiles, you won’t get lower than around 15 degrees. I think you’re going to struggle to get reasonable head room below the roof trusses without going higher with the roof. Why have you restricted it to 2.5m?

Are you sure it’s exempt from both Planning & BR’s? Is it detached? If it’s attached to your property, you must meet certain criteria to be planning exempt under permitted development but it will definitely be subject to BR’s unless it’s a conservatory/porch or car port.

Chameleon · 19 Aug 2011

Sorry for the confusion. It's detached and 1m in from boundry of the plot. Because of it's size i.e. max 2.5m height at external apex of roof, it's exempt from building regs and planning permission. That's been confirmed by the local building control dept.

From looking around, it's similar to some of the larger garden sheds/studios on display at the likes of B&Q.

Internally, it doesn't have to have a flat ceiling, it could be apexed, but I suspected I might be struggling with pitch and tile types, which is why I'm looking for advice.

Richard C · 19 Aug 2011

OK, just making sure you’ve checked it out.

As I said, if using conventional tiles you going to need a 22.5 degrees (or not much less) roof pitch which @ 2.5m max, allowing for truss depth & plasterboard, I reckon will reduce a 2ft strip of your internal wall height down to just over 5ft on the 12ft side & even less on the 14 ft side. I’ve only done some very rough guesstimation & you really need to draw it out accurately.

The other alternative is to go to one of the specialist reduce pitch tiles;
http://www.forticrete.co.uk/products/40/centurion-low-pitch-roof-tile.html

But I’ve no personal experience using these; I believe they can be expensive & difficult.

I reckon you will have to make your own trusses on site.

Chameleon · 19 Aug 2011

Many thanks. i really appreciate your advice.

nickjb · 19 Aug 2011

If it is more than 2m from the boundary you are allowed a bit more height. Building regs only really counts on area, not height.

More here
http://www.planningportal.gov.uk/permission/commonprojects/outbuildings/

I doubt you'll get a tiled roof to work. You really need some kind of flat roof system. I've just gone through the same process, in the end we applied for planning permission for a taller buidling and it sailed through.

tim00 · 19 Aug 2011

Well, perhaps they do things differently round your way , but my limited experience is that BCO will visit and take a keen interest in any such structure, Bldg Regs or not.

Richard C · 19 Aug 2011

I’ve approached this purely from a building & BR view point &, as I said, I’m not a pro roofer.

In the light of nickjb's post, it might pay you to go to PP & allow you to raise the ridge height just enough to accomodate a 2.1 wall/truss height. If you decide to stick with 2.5m, it would pay to make a more specific post in Roofing & Guttering for advice about reduced angle tiles as I know there are at least two roofers in there that should be able to help more specifically.

theoldun · 19 Aug 2011

Chameleon said:
I'm building a single storey in my garden which will be 14' wide x 12' deep

It will be constructed of brick and block and will be used as a studio, so I'm flexible in terms of the final design.

No comment ref planning or regs.

12 foot = 3660. Assume 300 cavity wall = 3260 overall plates =1630 half span. Say 12.5 degree pitch = 361 rise.
Overall height from highest point of ground to top of ridge.
Floor level above ground level. 150
Storey height 2100
Rise to setting out line (hypotenuse) 361
Rafter above setting out line Say 67
Tile and batten Say 65
Ridge say 75
Total 2818
Which is no good to you.

You could get away by door and windows in flank walls.
Throw steel across ridge, drop plate down to 1500 with vaulted ceiling at 22.5 degree pitch. This would give you a height of 2565. You may just about get away with that.

Or plate 1650 with 15 degree pitch with raised tie joists at 2100 storey height. This would give height of 2477.
Redland Regent Smooth go down to 12.5 degree
oldun

Chameleon · 20 Aug 2011

What height would I need to got to to get a reasonable pitch for tiles?

Blagard · 20 Aug 2011

The photo below is of a building that did not require Planning or Building Control approval - It pushed the limits on all! - It is built of blockwork, possibly cavity (you can see the window reveal is fairly deep), the outer blockwork has been finshed with a pvc cladding system. The low pitch roof is simply felt. UPVC door and window. It is at least twice as deep as the width, so you can only see half of it in the photo. I know it even has central heating extended from the owners house!

I just thought that maybe this is what you should be thinking of if you really don't want to get BC and Planning involved.

View media item 36741
EDIT: Noting your comments in the recent post below I think you are making the right decision. With a solid build below roof, it would be a shame to not get a roof of equal quality and lifespan.

Chameleon · 20 Aug 2011

Thanks for that. I'm not particularly trying to overt the the local authority, but I'm limited to garden space and if I come in from the boundary to 2m, the building will encroach a little too much into my garden.

After your advice, I think I'll stick to the same size of building, but go back to planning to enquire about increasing the height to allow a more ample pitch. I'd much prefer a tiled roof, than one done in felt. Particularly as sound proofing and security are of great concern to me.

Deluks · 20 Aug 2011

Felt roof would be more soundproofed than tiles, think of all those gaps.

Asphalt shingles on a double ply or OSB boarding, even better.

No ones gonna break in through the roof! And if they did, having to pull up a ply roof would soon put them off.

Richard C · 21 Aug 2011

Blagard said:
The photo below is of a building that did not require Planning or Building Control approval - It pushed the limits on all!

Presumably it was built before October 2010; it would not be exempt from BR’s now. Difficult to see in the photo but it looks to be closer than 1m to the boundary fence; the heating system must also be completely independent now, not an extension of the main building; it also looks to be very close to if not larger than 30sq/m & if that’s a timber roof, would fail the “must be constructed from largely non-combustible materials” condition. The regulations changed in October 2010, so it may have got by before then, particularly regarding the heating system.

I assume the gas bottles are for a stand alone appliance & not associated with the building as their location under that window would not comply either.

Blagard · 21 Aug 2011

Richard C said:
Presumably it was built before October 2010

Yes I am sure it was - I think the neighbours complained about it when it went up, so I would not be suprised if various LA officers have seen it.

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Single storey extension

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