Low Pitch Metal Tile Sheeting Roof Build

[brewhut]

Hi All,

I’m at the roofing stage of my brick shed, thanks to knowledge gained from this forum, thanks all

It is made ½ brick (single skin) with piers and has a span of 2.6m and is 7.8m long.

Due to the fixed upvc door height in the side wall being 2030mm (with sill) and only being able the have a maximum height of 2500mm as it’s near a boundary. Sets the roof pitch very shallow
(I don’t want a flat roof)

The wall plates are already in with a couple of straps only, I will add the rest when I know where the rafters are going, so they don’t get in the way.

I was looking at tile effect metal sheeting (like Masona’s), the one I found will go down to a pitch of 5°.

I’m thinking of making a cut roof for this, it’s not a house or an extension; I look at it as like a garage similar to the concrete sectional ones that have a simple roof, some even have tile effect sheets. I’m only a DIYer but if I take my time and do everything correct with some guidance, I’m sure it could be done. I hope I’ve got the terminology correct for all this!

The roofing sheets are about 11kg/m2 so, 2.6 x 7.8 = 20.3sqm x 11kg = 224kg + ridge, barg + all wood for trusses etc. say around 300kg unloaded. The roof sheet profile is about 30mm high.

I’m thinking of having 6 Rafters 75mm x 50 at 1.2m centres, that would do 6m leaving 0.9m to each gable. The gables will be built up in brick. I could do with birdmouths at 25mm deep just to keep the eaves height down. Ceiling joist of 100 x 50 at the bottom of each rafter pair making a truss. A Ridge beam in the middle that would have to be joined somehow to get +7.8m. I will make two separate trusses on the gables for the bricks to go in. Purlins/batterns of 50 x 50 at ridge, middle and eaves to screw roof sheets into (38mm screw). Maybe some hangers in middle of trusses

If someone can give me some guidance to the above, bear in mind the eaves can’t go too high and I need a 5° pitch. The eaves will increase by 2/3 rafter + battern + roof profile and ridge tile at ridge.

I’m not sure how it will all be fixed There seem to be many ideas out there. As long as the structure will handle the total loads + snow

Any constructive ideas/comments would be greatly welcomed

 

[masona]

only being able the have a maximum height of 2500mm as it’s near a boundary.

I'm assuming it's less than 2m from the boundary? You would've been okay before the new rules Oct 2008! What's on the other side of the boundary?

Sets the roof pitch very shallow

A quick calculation you'll need 3m height to get 15°

If someone can give me some guidance to the above, bear in mind the eaves can’t go too high and I need a 5° pitch.

The problem will be almost looks like a flat roof
Can you not pitch the other way with my calculation will be approximately 20° then you can use roof tiles

 

[brewhut]

Hi Masona,

Thanks for you reply.

The shed is next to my neighbours fence boundary (I get on with him ok) the other three side are no problem.

I was going to use Versasteel like you and got a good quote from Paul. Their system is ok for 10deg, but not below. This other system can handle 5deg min.

don't understand about pitching other way ?

I'm not sure about calculations, here is a diagram of the apex roof idea:

It shows just half of the span for an apex roof, does this look ok

 

[masona]

Will do a drawing, can't get the scanner to work at the moment, just bear with me

 

[SASroofer]

I'd just use a corrugated sheet system, eliminates problems like headlap and its a hell of a lot cheaper than metal tile systems.

 

[theoldun]

Brewhut, Before I go any further, what size wall plate have you put on?
You say door frame is 2030, but drawing shows 2200 to top of plate.
oldun

 

[masona]

I'm trying to pinch minimum height everywhere I can to give you more pitch height and this is the way I would do it, 18mm exterior plywood onto the rafters and drop the rafters flush to the top of the wall plate if possible with joist hangers, you then can fix the metal sheeting anywhere on the plywood, roofing felt on top of plywood, if any rain leak will run out to the gutter, see if you agreed with me on the angle pitch of 10 degrees which you then can use Versasteel sheets

 

[brewhut]

Thanks everyone for comments.

Masona, thanks very much for taking the time for your solution, much appreciated.

Looking at your materials thickness gives about 18mm + 55mm = 73mm + 2200mm = 2273mm.
2500mm – 2273mm = 227mm, Tan -1 (227/1300) = 9.9° Pitch

Yipee

A couple of questions have popped into my head, hope you don’t mind:

Would I still use a ceiling joist next to the rafter to make a strong trangle

Can I fix rafters on the inside edge of the wallplate, will the forces try to twist the wallplate/wall inwards

If I had some kind of bracket that hung on top and was shaped like this
....__
__|

the weight would be on the wallplate.

I’m a bit worried about the extra weight of all that 18mm ply, with it only being half brick walls.

I’m not sure how heavy versasteel is per m2, but it was the 0.7mm version I was quoted for.

When I know what roof sheets I’m going to be using, would let me place battens at the exactly the right positions on the rafters, I could always shape the last batten on the wallplate for the slope, this would cut down the weight of using ply. The other roofsheet is 30mm if used with say a 38mm batten would give 68mm around 10.2°, what do you think




Oldun, the eaves are 2200mm. This is one brick from ground to DPC, mortar, 2030mm door frame and sill and wallplate (100mm x 100mm). I don’t know why the builder has used a 100mm high wallplate, 75mm would have given me 25mm more to play with. The wallplate is directly on top of the 2m wide upvc doors and 2m wide upvc window and is acting as the lintel, maybe that’s why it’s so big.

 

[masona]

I’m a bit worried about the extra weight of all that 18mm ply, with it only being half brick walls.

Not if you design the roof trusses correctly, now thinking about it, I have done this many times, might be best to have the roof rafters made by the gang nail trusses company which I find can be cheaper than making it yourself and will be a lot easier for you to do, just give them the drawing info from wallplate to wallplate and height etc and they will do the design and calculation for you, they use a lot smaller size timber because of the clever design of these type of roof which again can give you a bit more pitch.


You don't have to use plywood, just thought it would be easier for you to use instead of the hit & miss with tiles battens and would be screw down onto the wallplate

ps: give and take, where do you take the maximum height of the roof ridge from what level of your garden

 

[brewhut]

Interesting that Masona,

A while ago I contacted a truss company, Cheshire trusses or something with the dimensions and they said their machine couldn't cut them for some reason.

Have you any details of the "gang nail trusses company" or a website address and will they be able to make something that mounts on the inside edge of the wall-plates.

I looked all over the web 'planning portal' etc for height measuring definitions. In the end I used an old booklet "Planning, A guide for Households". On page 22 it mentions 3m and 4m heights and measurements are given on page 19. Page 19 says:

"You should measure the height of buildings from the ground level immediately next to it. If the ground is uneven, you should measure from the highest part of the surface".

hope this is still the case and valid

 

[masona]

A while ago I contacted a truss company, Cheshire trusses or something with the dimensions and they said their machine couldn't cut them for some reason.

They properly wasn't interested in a smaller job(?)

Have you any details of the "gang nail trusses company" or a website address and will they be able to make something that mounts on the inside edge of the wall-plates.

I'm lucky I have a local trusses company to me, I don't know what is in your area, but they will deliver and they will advise you the best way to go as can be done with difference ideas, keep searching!

I looked all over the web 'planning portal' etc for height measuring definitions. In the end I used an old booklet "Planning, A guide for Households". On page 22 it mentions 3m and 4m heights and measurements are given on page 19. Page 19 says:

"You should measure the height of buildings from the ground level immediately next to it. If the ground is uneven, you should measure from the highest part of the surface".

hope this is still the case and valid

I love this! alway been a grey area and that's why I mentioned it

Get load of earth around it and now you've got a sunken outbuilding which should give you little more height

I was also told and haven't done a search on this, if the outbuilding is over 7yrs old then no one can object, another grey area, how old is the outbuilding

 

[theoldun]

Brewhut. Where do I start. FinkTrusses. Top chord sits on top of pitch cut of bottom chord and these are normally 35x97, Even if top chord was reduced to 35x72 the raking cut at the node for a 10 degree pitch is far to long to be practical. This is the reason you can not get trusses made up to 10 degree pitch. Sketch a fink truss up with 10 degree pitch, and you will see yourself.
In our opinion 50x75 rafters at 1200 centres not acceptable. Centres to big.
In our opinion 50x50 battens over 1200 centres, not acceptable. Centres to big.
In our opinion rafters hung on timber to masonry or timber to timber hangers on inside of wall with or without coupling, not acceptable. Insufficient lateral restraint to stop creep on such a shallow pitched roof.
Will tell you how we would do it, then you can make up your own mind. Would point out though, this will not be cheap and has a couple of disadvantages.
Ceiling joists 2400 long 47x125 regularised to 47x122 at 600 centres fixed to 100mm wall plate with Simpsons JHA timber to timber joist hangers with adjustable height strap. Joists cut tight to plate to stop any axial twist to plate and straps bent over plate and fixed to top of plate. All nail holes to be filled with 30mm square twisted galv nails. With the joists hung this way, there is no lateral thrust, only downward, for which the hanger is designed.
Firings 1300 long out of 47x220, (you may be lucky and get 47x225 but normally they only stand up to 220. You can easily cut them your self, Mark them out, nail a guide down them and push skil saw down guide. Fit new blade before hand.
Drop and fit firings on to top of joists. Glue and screw couple of 25x100 soldiers up each side.
This will give you adjacent 1300, opposite 220, hypotenuse 1318, angle 9.6 degrees. Therefore 2200 top of plate + rise 220 = 2420, leaves you 80mm for 25x50 battens sheet and ridge.
You could increase your pitch to 10 degrees by planting a 50x10 batten on to 220 firing to give 230 depth which will increase your rise to 230, but will loose 10mm on the balance above.
Disadvantages. More costly. Storey height inside only 2075, but bear in mind standard door height is 2040 so there is still sufficient headroom.
Advantages. Ease of assembly. All components are doing the job they were designed for
Your choice.
To the best of my knowledge. The maximum height of building should be measured from the lowest finished ground level adjoining the building.
oldun

 

[masona]

On the 2nd picture that's where the joist hangers comes in with extra added supports, pity I don't near you, your roof won't be heavy compare to roof concrete tiles. A half hip roof should gain a higher pitch. However, I gave it a lot a thoughts and I think the easiest within your capability, (not sure what you can do!) is to have metal angle iron trusses made welded up and you could do away with the wallplate as well then maybe 4"x1" batten across for the metal roof sheetings, also you could have a small bracket made up welded on the end of the trusses on either side of the wall which can be covered by fascia board, they do these type of angle iron trusses on concrete slabs garages/sheds

 

[brewhut]

Thanks oldun and masona, much appreciated, sorry for delay still witering and thinking/drawing crazy diagrams, will be back soooooon, it's becoming clearer

Thanks, brilliant advice, Brewhut