another request for help on roof design please

[devonwoody]

I have in the past always looked at replacing my workshop roof (at present flat roof corrugated asbestos).

Seen one or two new workshop designs here on the forum lately with pitched roofs and note that they have not had joists across the walls.

I am asking for advice as follows.

Can I have a low pitch roof (Not heavy tiles) and avoid those long lengths of joists ? (the clear span is 5.5maters, which means special delivery and high costs)

So I am posting this plan, the area marked red are existing joists tied into walls.

Could I put on new wall plates of 4xi2 (Marked blue) and then a low pitch roof without long joists but collars higher up the rafters?

Any advice appreciated. ( A new flat roof was quoted this year at £2500 but the specification was unsatisfactory to me although I could manage the price)

 

[monkeybiter]

When I extended my workshop a few years ago I replaced my pitched flat roof with a gable roof. I wanted all the headroom I could get and didn't want any cross members, so I put an I-beam as the apex [suitably supported] and the joists 'rest' on the beam at the top and the wall at the bottom. The joists are 'tied' together at the top in pairs, so there is no outward splaying force at the wall top. The roof width is about 16' and the length of the beam approx 18'.

 

[SketchUp Guru]

I would think you could do what you propose.

I just did a quickie drawing for my own edification. I've drawn 4x2 trusses with a 3:12 pitch (common around this area where we have high snow loads to contend with.) That works out to be about 14°. The top of the collar ties is a foot below the bottom of the apex. Plywood gusset plats glued and nailed over the joints would add a lot of strength.

 

[devonwoody]

Thanks Dave, I will print out your two drawings (or perhaps you could email them as another of your favours) and ask the builder who quoted for the flat roof earlier this year for another quotation.

It does alter the frontage aspect, so do I have to apply for planning permission does anyone know? I might be able to hide it because I have a brick gable frontage at present and roof might not be seen behind if necessary.

 

[SketchUp Guru]

E-mails sent. :wink:

 

[devonwoody]

Many thanks DaveR, I will print them out and have a chat with the builder and get him to quote.

Let you know what happens.

 

[SketchUp Guru]

Hi DW,

I was just thinking about your roof and wondering how it worked out. With your current weather, I think I would got for a slightly steeper roof than what I drew and perhaps use timbers of larger section. Maybe 6x2 instead of 4x2 as I drew.

 

[devonwoody]

Weather not so bad down here in the S.W. (Devon), we occasionally get a heavy snowfall, last one 1963 around 5ft but nothing heavy since.

Builder I think must be away on a job somewhere, not seen, he visits his parents usually who are neighbours, so will discuss with him when available.

BTW around minus 6C today, the frost looks like snow. :ho2

 

[SketchUp Guru]

I'm glad you don't have all that snow everyone else is having.

-11°C here right now and that is listed as the high for the day. It's not even 6 am, either. Snow is coming down in big fluffy flakes right now. Should make for a greasy drive home.

I'll be watching for updates on your shop.

 

[reynotted]

I think a steeper roof style is better for your house for that kind of weather in your place. The roof should be stronger than a normal roof. The frames should be bigger and stronger than usual.

 

[devonwoody]

My building (garage) has foundations of an unknown specification, and the walls are only 4" concrete blocks on what might be a concrete raft only.
And to be honest whatever is constructed, am I likely to go out playing in there at my age considering weather like this. So perhaps I am dreaming again.