Ideas for construction method on new summerhouse

[garyo]

The rear extension I built last year suffered from this - 4.5m span on the extension, 5.6m on the main house. This meant that my ridge plate was forced slightly off centre and gave me unequal pitches. In that situation I ended up with slightly different soffit depths, but you wouldn't know when you look at it from the ground.

I expect the height of this ridge beam being so shallow will exaggerate the effect though.

Great videos - still watching them.

Gar y

 

[theoldun]

Gary,
Got me head together now. Read your PM box.
Two questions what pitch do you want?
Have you not considered flat roof with EDPM?
Regards oldun

 

[garyo]

The existing garage roof is flat and leaks, so I thought I'd take the opportunity to get myself some extra storage, and at the same time 'do it properly'.

I did have a look at the idea of EPDM on a pitched roof, but it's fairly expensive stuff and so there's not much in it when you look at the cost of the OSB and EPDM, versus the cheap end of the plastic/tiled roof scale.

Anyway... my garage already has 40 3.6M lengths of 100mm x 50mm C24's so I'm kind of committed to this approach now!

To answer your question on pitch - I've not worked it out, but don't want to go above 1300mm between top of wall plate and top of ridge so that the garage matches the neighbours that are on either side.

Gary

 

[theoldun]

Gary,
Looked at stud work, appears neat tidy and stable. but wish we had got to you earlier.
Studs should always be as close as poss to sit underside of rafters. We lay the bottom plate out dry and set out our roof and doors and windows before we start to stud.
Windows. If you have a window 1200x1200 then we leave an opening between two studs of 1350. Plant a short stud long enough to include a horizontal stud on the top to give you your cill height, stud out below cill plate to suit plaster board sizes. On top of cill plate fix two studs to main studs 1210 high. The 10mm will give you clearance for window. Nail or bolt up two 50x150 to form timber bressmur to plant on top of these two studs to support roof
However as you only show a 2230 storey height on your drawing so you are frigged for getting a 150 bressmur in. Alternatively, use 1050 deep windows or lower cill height accordingly. The remaining gap left is for 22x say 150 PSE as side cheeks to windows and to protrude 12mm past claddiing.if studs are 47mm instead of 50, decrease opening accordingly.
Your doors are the problem, once again you show 2230 from floor level to underside of double plate.Your frame will be 2100, so you have not got room for a decent timber bressmur. We would have put two 50x200 bolted together over a 2400 opening
Suggest you cut the bottom plate out of the double header plate. And make up a 150 deep flitch beam with 10mm steel plate, and jiggle the insulation on the inside of the flitch beam.
Frame up your door opening all as windows, a stud against the side of main stude to sit bressmer on and a gap for your side cheeks. Shim between bressmur and top plate as required under where rafters will sit.Gary, have no calcs for flitch beam over that span , is only what we feel may be sufficient.
You may be able to lower the threshold of the door and still keep mat clearance, Can not tell from your drawings.
Regards bottm plate. Do not rely on your present fixings. From medium duty restraint strap, put a 90 degree 90mm long bend at the top allow for depth down to oversite put 90 degree bend 200mm long in the opposite direction and screw down into concrete, side and top of plate. Every corner and metre between and both sides of door opening. Let us know what stage you are at for roof..
Regards oldun

 

[garyo]

Thanks for the long reply - still digesting it. I've been scratching my head about that span for a while.

My door frames are 2080 high including cill, so from the 2230 gap that leaves me with 150mm. How about I take the bottom of the double header plate out and then fit a doubled up 200 x 50?

It'll be tight but I think I can just about do it - will go re-measure everything.

 

[theoldun]

I've been scratching my head AND ME AR*SE about that span for a while.
How about I take the bottom of the double header plate out and then fit a doubled up 200 x 50?

Do that. That is what we suggested. You have still not give the pitch you want.
Regards roof, we are only going to give you suggestions You know enough by now to sort it out yourself.
Did we explain pitch line and HAP to you on last roof you did?
Pitch ASAP.
Regards oldun

 

[garyo]

Thanks - I'll get the pitches to you later tonight.

 

[garyo]

On the part with a 3800mm span, which already has 200mm x 50mm joists at 400mm centres:
- Span minus 50mm ridge plate width= 3750mm = so an effective run of 1875mm
- Rise = 1163mm
- Pitch 32.5 degrees
- HAP=177mm plumb cut *0.66=117mm

On the part with 4500mm span, which ideally I'd like vaulted, perhaps with a couple of doubled up beams or collar ties to prevent spread:
- Span minus 50mm ridge plate width=4450mm = so an effective run of 2225mm
- Rise=1170mm
- Pitch=26.5 degrees
- HAP = 167mm plumb cut*0.66=110mm

I've been thinking about the position of the doubled up rafter beams and king posts. Obviously the beam bearing on the bressemer over the doors isn't ideal. Perhaps I'm better off with collar ties?

Untitled

• garyo
• 7 Aug 2014
• 1

Untitled

• garyo
• 7 Aug 2014
• 1

 

[theoldun]

Gary .
Before we forget sheath stud work out from top of plate to bottom plate before you start roof. Over the door bressmur, suggest you run threee beads of sticks like sh* te to laminate sheathing with plenty of nails or screws We would do the same on the back and cut the back of the PL4000insulation accordingly to allow for thickness of sheathing. This will make the bressmur much, much stronger. Do not forget to add sheathing to overall span measure
We did some rough figures for roof purely to get approx difference in the pitches. We did not allow for HAP or half thickness of ridge board. We do not appear to be on same wave length as your figures, so will quickly run through it again. Take the sun room. Okay with your span, but not allowed for sheathing as do not know what you are using. Forget about the odd 0.5 degree call it 26 degrees, 0.5 is neither here nor there.
On a 26 deg pitch and a span of 2225 , sheathing excluded the rise is 1085 to the PITCH LINE and length of rafter from top plumb cut to heel cut is 2476. The PITCH LINE is the hypotenuse of the external top corner of wall plate and depending on depth of rafters being used is two thirds at 90 deg sown from top of rafter and top of ridge board. Will explain further tomorrow
Gary will post this now as want you to get your sheathing done before starting roof . Will be back tomorrow
Regards oldun

 

[theoldun]

Gary,
We are only a few coppers apart , so briefly, a 50x150 rafter at 26 deg will have 64 deg top plumb cut 167 long. A heel cut 54 deep and HAP of 113 and seat cut of 26 deg and 110 long.
True hypotenuse is 1085 plus HAP of 113 makes total rise from top of p[ate to top of ridge 1198. We are in rush today so CHECK our figures. Jiggle depth of heel cut and seat coat about to try and get as near as poss the same HAP on both roofs,
Collar Ties one third down, half down, two thirds down.
One third down will not prevent spread on vaulted roof. They are there to lock the opposing rafters to the ridge in high wind zone areas and for unequal snow loading No point in going into the other two as they are of no concern. In sunroom suggest a collar one third down every pair rafters. On vaulted ceiling rafters should be birds beaked on to top of structural beam either timber or a USB
Back in the 50s before we had builders metal work, we used a joint called the London Tenon. We suggest you use this on ridge board and rafters
Will explain. On top 67 deg top cut place small length of 25x50 at bottom of rafter.with the 50mm parallel with rafter cut mark it out cut it out and this will hang your rafters on a 25x50 batten laminated and screwed to to the position required on ridge beam.
King posts and tie beams, odds and sods suggestions tomorrow
Regards oldun .
.

 

[theoldun]

Gary
In your post dated 31 July you said you have 40 3.6 50x100

In your PM dated 31 July you said you have £600 of 50x150

Please confirm what size rafters you are using?
Regards oldun

 

[garyo]

They're 50 x 150!

 

[theoldun]

Gary
Received PM
Suggestions. If you have laminated sheathing both sides of bressmur then we feel it will be strong enough to support the double beam coupler in position shown on drawing.
Laminate and screw double beam 50mm up and 50mm with 80x6 screws at 450 centres, same other side but staggered to first side. If you have router, run V joint along the bottom join and a moulding down each bottom arris. Top as well if you wish. King post . Two number 50x100 laminated together and V jointed as before and edged as before on four corners plus the bottom to match top moulding if you have run top. Notch top of King post 50x50 and screw to ridge and to coupler beam. You can add a couple of splay beams to King and coupler if you wish to spread point load of King. and roof
Collars 50x100m one third down to every pair of commons. The weak point of roof over sun lounge is possible spread and creep to the hip on flank wall. If you are worried about this say so and will come up with something. If you have not got a router will PM you our address and telephone number and you can borrow one of ours complete with cutters
You will need similar king post support of both ridge beams at hip and valley intersection over garage.
That’s about all for now, phone me if you get stuck.
Did you understand London Tenon
Regards oldun.

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[garyo]

Thanks - presumably the V join you propose is cosmetic only, to hide the double radius that would otherwise be there?

OSB is all fitted now other than the laminated parts over the bressmur. I've been fighting the rain for the last week though, so not very productive.

 

[munchingB]

hi garyo-can you post some pics for the rest of us to see?

sure im not the only one interested in seeing what you are talking about


cheers : )