Large mono pitch workshop construction advice needed

KevinD

We are planning to build a large (app20x14") timber workshop in back garden. Because of our requirements we need it to be "pent" construction with 12' wall at back sloping down to 8' in the front.
Can anyone give some advice about the practicalities of constructing this? We are very handy but not that clued-up on construction. How many internal tie-ins will such a roof need for instance?
The other issue is the height of the roof - will it need to be tiled at this height to fit within the scope for no planning permission required or will an onduline or similar roofing cover be sufficient?
This is not going to be just a shed as we are insulating the walls and building with a 4x2 framework, so quite a lot of weight involved.

muffler

This could go here or in DIY but I will leave it be for the time being.

Are you sure you dont require planning permission?

Mellor

Under 25 sq.m should be ok, depending on whats already happened, and the garden size.
But 20'x14' is close to this, about 24sq.m off the top of my head. there is also a height requirement, but i can't remember what it is at the moment, this could also be close to the limit.

muffler

Well 20' x 14' = 26 sq. metres so thats over the limit.

The max. height for exempted sheds is 3 metres for a mono-pitch roof and thats with tiles or slates so thats another problem.

I think the OP has to determine at this stage if planning is required or not and the best way to do that is to apply for a cert. of exemption from the local planning dept.

galwaytt

Just found this text on my CoCo's site:

"You can build a garage, carport, shed, greenhouse, kennel fo r domestic pets, etc., as long as it does not extend out in fro n t of the building line of the house and does not exceed 4 metres in height, (if it has a tiled or slated pitched roof), or 3 metres (if it has any other roof type). The floor are a limitation for exempted development is 25 square metre s . The structure may not be lived in, used for commerc i a l purposes or for keeping pigs, poultry, pigeons, ponies or horses. Garages, sheds, etc. to the side of the house mu s t match the finish of the house. You cannot reduce the open space at the side or rear of the house below 25 square metres ."




Btw, I'd adjust the size of the 'shed' to be a smidgeon under the exempt size, just for safety, nothing worse than a pedantic pp person measuring from eave, or gutter overhang, not the wall dims.........

As for build, we got asked to do something kinda similar lately, but on a bigger scale. 30m x 10m, clear span, conc floor, but demountable in future, no partitions or pillars. Trusses - greatest thing since sliced bread.

pics if you want.

KevinD

Many thanks to all for replies.
We are aware the limits for planning - dimensions are rough exterior dimensions so that should be fine. Yes, roof covering is a proplem with such a high pitch. Will have to be tiled.
Our main concern is the construction of the roof as we need at least 10' (preferably 12') clear head height in places. The old fashioned rafters construction is therefore preferable, but we need to sort out where and how many truss-type ties we need inside at those dimensions. The other worry is the sheer size and weight of the tall back wall.
We are also considering an alternative roof structure - app 12' high pitch off-set to one side (not sure if this makes sense). Again rafters would give us the head height inside, whereas trusses probably wouldn't.
galwaytt - pics will be very much appreciated!

muffler

A portal frame structure would sort it out. In any event you really should get an engineer/technician to take things in hand.

galwaytt

exterior - 3m ridge, on a 10m wide building, so a 3m on yours would be no problem - but that's external dims - why do you need 3m inside?
If you don't have a 3m high door....it's kinda.........er, irrelevent ?

This walls of this building were just made of 8 pieces in it's entirety.



Interior - trusses at 3m centres.




also, interesting link for you, on trusses, generally: http://www.tra.org.uk/technical.php

KevinD

Galwaytt, Many thanks for images - quite impressive size! We are probably not interested in metal though - what is the pricing like in comparison with timber?
We need the height for storing and handling lengths of mouldings vertically. So thanks for your comment but not entirely accurate - we know our business!

Yes Muffler, obviously a portal frame would be ideal, but is this not very expensive? We only need a space of about 6' deep with that head height inside. This is why we feel a rafter roof would be ideal as, with the correct size timbers, we could space the "trusses" quite far apart, if the walls are strong enough to hold the weight of the roof. Is this correct?
We are happy to get a carpenter/builder to do the main frame construction, but are exploring the options for ourselves before we go ahead. So all your advice is welcome.

galwaytt

actually, building isn't metal..........but I digress.

I had my own 12m x 8m garage and my sunroom done in metal portal frame 2yrs ago almost. Garage frame - galvanised - was Eur 3.5k iirc, erected.......including purlins etc.

Sunroom, 5.5 x 5, again galv, was ..........Eur 800?? I erected & welded that myself though, but got a local mfr to make the parts and galv them. I made some of it 'bolt-up' to ease installation. I then did in-fill between the columns with walls/insulation etc.

A light galv purlin would easily span your workshop, and you could fix an insulated panel roof to it easily - 14' isn't that big, really, and the roof would be light.

I think you might be surprised how easy and fast a simple portal frame would be.................

KevinD

I was referring to the trusses being metal. My husband is comfortable with wood and we wanted to do some of the construction ourselves and certainly want to clad the outside in wood. The metal frames do seem very reasonable and practical though. Is it possible to combine it successfully with wood, osb cladding and possibly tiles on the roof? We were also looking at onduline cladding for the bits that won't be visible. Any advice or ideas?

While we're at it; some of the more modern (and very expensive) garden room manufacturers skip the concrete base and build straight onto a metal frame. Any experience with this?

Many thanks for your ideas so far.

galwaytt

just off my head - 100mm box frame. 45 x 100 treated wall plate on top all round. Drop on panels (either insulated, or built-up insulated, e.g. http://www.newellroofing.com/roofing.asp ) to span in one go.

Walls - well I wouldn't build a single skin uninsulated building of any kind. If you do build up a panel around the frame, wrap it in breather membrane (Tyvek/Solitex, etc), then cross batten it with 45mm treated battens, and put your preferred finish on that (e.g. treated shiplap siding, alu, steel, aquabord, durock/whatever).