Summerhouse/workshop...

[chirpychippy]

May I ask a couple of questions regarding my own design for a summer house/workshop in my garden.

I'm intending to build a "stick built" building measuring 5.5ntrs x 3.5 mtrs. Now I'm pondering what size timbers to use for walls. I have designed it using 5x2 studs and plates, but am wondering if 4x2 C24 would be sufficient "Cost" The exterior will be clad in 11mm osb, with a breathable membrane, counter battoned and then clad, so from a rigidity aspect, it should be rigid.

The second question is insulation, I've designed it for 100mm PIR in the timber base, 50mm PIR in the walls and 75mm in the cold roof which is flat, 75mm will give me a continuous air flow of 50mm.

Other than the base I wondering if Rock wool will be sufficient in the walls and possibly the roof, after all its a summerhouse/workshop I'm not going to live in it?

Thank you.

 

[Deluks]

4x2 C16, or even 89mm CLS will be fine, you can always double them up where you need extra strength or under load points.

Obviously more insulation is better, you could save a bit of money by using EPS in the floor (polystyrene instead of the yellow stuff.
Rockwool in the walls will be fine and slightly better sound insulation.
Save the PIR for the roof.

No reason not to have a warm roof over a cold roof?

 

[foxhole]

3x2 are fine once the inner skin is boarded should be very sturdy , you could use same osb on the inside as it’s sturdy enough to take shelving etc.

 

[chirpychippy]

4x2 C16, or even 89mm CLS will be fine, you can always double them up where you need extra strength or under load points.

Obviously more insulation is better, you could save a bit of money by using EPS in the floor (polystyrene instead of the yellow stuff.
Rockwool in the walls will be fine and slightly better sound insulation.
Save the PIR for the roof.

No reason not to have a warm roof over a cold roof?

I've chosen cold roof as the building will be close to the a boundary fence and am governed by the 2.5mtr maximum height, the ceiling joists need to be 7x2 for the span, if I made it warm roof I'd have a fascia board that's about 300mm which ruins the finish imo.

But that said I'll draw it to scale to get a feel, warm roof is damp sight easier than cold though.

 

[chirpychippy]

3x2 are fine once the inner skin is boarded should be very sturdy , you could use same osb on the inside as it’s sturdy enough to take shelving etc.

It's getting less expensive now, I'll go 4x2, the reason being is I'm putting a flitch beam over the bifolds to support the roof, 45mm + 10mm + 45mm equals 100, just need to hide the bolts somewhere, actually will go 5x2 on the front.

Thank you.

 

[mrrusty]

There's another similar thread here https://www.diynot.com/diy/threads/cavity-blockwork-vs-timber-frame-garden-room.623705/ have a look at my post in this thread linking to my build using SIPs. They potentially give you another option. When you weigh up the costs of timber, insulation, sheet materials plus time IMHO SIPs are almost a no-brainer. an 8' x 4' 122mm SIP is £90 inc VAT - absolutely perfectly flat and rigid, as opposed to framing up in timber which needs careful selection to avoid all the twisted and banana pieces...

A quick calc from my merchants prices for 4x2 framing (9.6 m for an 8x4 panel - 3 uprights + top and bottom) + 2 sheets of 11mm OSB plus a sheet of 100mm XPS comes to £72, then you've got nails and time.....

OK not a true like for like because SIPs need splines etc, but there isn't much in it!

 

[foxhole]

I made my stud work for loft conversion using unbanded scaffold
Boards £12 for 3.9m which ripped on table saw gave three uprights and off cut for all noggins .

 

[mrrusty]

A 2.4m length of 4 x 2 in C16 is only £3.19 + VAT at my merchant so not much in it using scaff boards!

 

[chirpychippy]

A 2.4m length of 4 x 2 in C16 is only £3.19 + VAT at my merchant so not much in it using scaff boards!

Pray tell Squire whom is your supplier, my supplier has quoted £4.34 + VAT for 2.4mtrs of C16...........

 

[mrrusty]

It's a local merchant in Leyland, Lancs - https://www.cwberry.com/