Architect or structural engineer?

[the bear]

Afternoon folks
I'm going to be helping my father reroof his garage from 1960's concrete interlocking tiles to plain clay tiles. The current roof isn't pitched enough for the plain tiles so its going to be reframed steeper. This will also get rid of the bits with rot and old woodworm as well so its quite a big job but something he's wanted to do for years. Current roof is full of intermediate supports and he would like to get rid of as much as that as possible to gain as much open storage up there. He'd like to have a small door above the main up and over door to slide ladders long lengths of timer etc in. (its a double gable design) It won't be big enough to stand up in but should give lots of storage.
Pre planning advice says it shouldn't be a problem. My question is this though, it need designing properly as its a big garage. Does it require an architect or a structural engineer to design it (or someone else)? Happy to insert some flitch beams etc if need be to open the new loft up.
Resident architect/structural engineers/other knowledgable help appreciated!

many thanks

Mark

 

[Mike G]

Mark, just give me an idea of the span and I'll let you know whether it is within the scope of a mere architect like me, or whether you have to stump up for an engineer. A photo or two would be useful, and if you know what the current pitch is that would be useful too.

I'm not about until tomorrow evening, so you'll have to wait a bit for a full response.

 

[the bear]

Mike.
Thanks for the reply. It’s 7.8m long and 5.5m wide outside measurements. The skin is a brick outer block inner cavity wall (it’s detached) so the span is slightly less than 5.5 given the ceiling joists sit on the inner skin. The pitch is about 25 degrees and needs to go up to 35 Which I reckon gives about another 1/2 meter of height up there. (Minus what will probably be bigger rafters) but hopefully much more open and useful space. Sorry don’t have any photos at mo still at work after a very long day
Many thanks
Mark

 

[Mike G]

I can design that for you. The biggest issue is the tie (ceiling joist), and what loading you intend to apply. Are you planning on boarding out the loft and using it for storage? Will the tie be at wall plate level, or raised?

 

[the bear]

Hi mike that’s great you can help. I need to check later, I’ve assumed the ties at ceiling/wall plate level and boarded but now you’ve asked I’m not actually sure. Would I be right to assume the 4 inch current ceiling joists/ties will need to be replaced as well as the rafters? Not a problem if yes just wondered. I’ll hopefully have the answers tonight.
Thank you
Mark

 

[Mike G]

Four inch ties over 5.4m+! Is it a gang-nail trussed roof? Are there 4 intermediate timbers forming a sort-of "W"?

The basic answer is no, you are going to end up with joists/ ties in the region of 200 to 250mm thick, depending on what you are planning for the roof void.

 

[the bear]

Mike
Yes I guess 4 inch ties was wishful thinking! I had assumed at the start the whole thing coming off including ceiling joists/ties, but thought I'd ask.

Back to your actual questions, ceiling ties at wall plate level. This is to make more volume of space up there and be able to crawl around in it as is possible now. As for boarding the ties/ceiling joists he has no strong feeling either way. Its not currently boarded save one tiny bit. What effect does boarding it have? Does it means the ties need beefing up? Boards would be nice as it makes crawling around easier but if it means bigger ties not sure its worth it. If its about what will be stored up there then there is currently a bit of wood some of which is mine, theres xmas decorations in boxes, a few other not that heavy boxes (otherwise wouldn't be able to get them up). He also stores his petrol power tools up there away from thieving hands (chainsaw, strimmer, blower). He wants to put his ladder in hence he would like the small door above the up and over door. As I said earlier if a few flitch beams would help we can do that.

Ive got some photos of the current if its any relevance, its quite hard to get a photo outside. Purely for your interest since they will be coming out also photoed the inside. I've checked and it is 4 inch ties. Theres also a 2x6 purlin each side, a 2x6 strutting beam each side (is that the correct term) and 4 of those W frames (1 at each end and 2 others evenly spaced). Those W frames make getting into the whole loft space a pain.

I'll put photos in next post

Mark

 

[the bear]

Photos attached

 

[the bear]

Photos have attached in reverse order that I added them, is this normal?
Mark

 

[9fingers]

Photos have attached in reverse order that I added them, is this normal?
Mark

That is because you have not used the "place inline" command to organise them and instead just left them dumped at the end of the post with dotted borders. In this case yes they appear in reverse order.
Check out the sticky on photo posting to see the full process.

Bob

 

[the bear]

Giving this a bit of a bump in the hope Mike sees it and is able to comment, or anyone else for that matter.
Mods is it worth moving this to the projects or workshop builds section where it would seem to be more at home?

Many thanks

Mark

 

[Mike G]

Humble apologies. I just missed this somehow.

The rafters are the easy bit.....195x45 @ 400 centres. 170x45 works, but is less commonly available.

The joists/ ties are more complex, depending on the weight of the proposed storage in the loft. 220x45 (C24) again bolted to the rafters at plate level works, but with nothing much spare for any weight. The way to get it to work as a storage area is to hang the centre of the joists off the ridge using hangers (vertical timbers) and a binder (a longitudinal timber along the line of hangers making the floor act as one). The hangers can be 95x45 bolted to every 3rd rafter at the ridge, and the binder 145x45, nailed to the hangers on top of the joists, and, crucially, strapped around each joist with galvanised mild steel strapping, using lots of twist nails.

If dividing the space in half with that line of central timbers isn't going to work for you, then you're into the territory of either an RSJ underneath running longitudinally under the centre of the joists, or, engineered timber I beams for the joists. Both of these solutions would require the input of a structural engineer. Crucially, if Building Control are involved, then I can't provide calculations. That's outside my professional qualifications and liability insurance. Again, you'll need a structural engineer in that case.

 

[the bear]

Mike,
Thank you for the reply, its really appreciated. So rafters is easy, thats good to know. We'd like to keep the loft unobstructed if possible and therefore avoid the hangers if possible (but if the other timbers becomes so massive to make it prohibitive then theres no point and be better to put them in, if that makes sense)

Though I have no issue with the theory of putting a steel in under the joists we're also loath to reduce the height in the garage. One day the up and over door will be coming out and some sort of bifold type door going in and we'd like enough head room to get a van or landy in there. I also think this would require an rsj above the up and over door and above the full width rear window (see earlier photo) to support it.

which brings me to the engineered timber i beams. Firstly I have no idea of cost of these so don't now if thats prohibitive from the start, but I think this is at first glance the best solution. Would we be talking I beams, metal web beams, glulams or something else? Also without asking you to do a calculation youre not qualified to do, as a rule of thumb would it be a case of a similar size beam to a normal c24 timber being used, but as its engineered it can carry a greater load, or do the engineered beams mean a smaller beam is required?

Many thanks for the input Mike

Mark

 

[Mike G]

.......which brings me to the engineered timber i beams. Firstly I have no idea of cost of these

They're very reasonable.

Would we be talking I beams, metal web beams, glulams or something else?

I beams, like this: http://coastalforestproducts.com/engineered-wood-products/nordic-i-joists/

Also without asking you to do a calculation youre not qualified to do, as a rule of thumb would it be a case of a similar size beam to a normal c24 timber being used, but as its engineered it can carry a greater load, or do the engineered beams mean a smaller beam is required?

:lol: You just asked me to do a calculation I'm not qualified to do. :lol: Generally, as I understand it, an I beam will carry quite a lot more load than a timber of similar depth.

 

[Mike G]

.......One day.......we'd like enough head room to get a .....landy in there......

Then you'll need a massive sump in the floor to collect all the spilled oil, enough headroom to put it on a lift, and an engineering hoist/ beam arrangement for the bi-annual engine-removing bonanza. Oh, and it needs to be wide enough that you can extract the broken half-shafts every few months. :lol:

 

[the bear]

I'm getting the feeling you're not a Landy/defender fan Mike, Landcruiser for you?

Thanks for giving me plenty to think about, I'll do some research on the I beams and see how much a structural engineer is going to cost me to see if thats the route to take.

Mark

 

[RogerS]

Mark, check this company out. https://www.jamesjones.co.uk/products-a ... ji-joists/

They do an interactive span table program.

If anyone is interested in how they make them then go here and look at the video at the bottom. Fascinating.

I found a local company who designed my orangerie lantern for me complete with drawings.

 

[Mike G]

I'm getting the feeling you're not a Landy/defender fan Mike, Landcruiser for you?.....

I love 'em really! In 1994/95 I drove the length of Africa in a Landcruiser. In 24,000 miles in some absolutely horrendous conditions the only thing that failed was the radiator cap. The Landrover (IIA-110) that was the other half of the expedition was a year younger than my Landcruiser. We rebuilt the engine twice, and the gearbox once (it still jumped out of 1st unless you sat holding the lever in place with your knee). We broke halfshafts, and every single piece of the suspension at least once. The door fell off in Zaire. It used more oil than petrol (I exaggerate), and could only manage 45mph (I don't exaggerate). The electrics were a joke, the ignition circuit sometimes needed working on twice in a day. Its brake lights melted descending a mountain. Wheel bearings lasted two or three months. The handbrake working on the propshaft is one of the cruellest jokes ever played by one man on another. The hand-throttle was in the passenger footwell, which isn't that handy if some wildlife runs into the road in front of you. The driver sits crammed up against the door on a boiling vinyl seat, bashing his elbow on the door every time he wrestles the steering wheel (unaided by power steering), and even with all the vents closed there are holes everywhere big enough to let the tsetse flies in to eat you alive. The starter motor failed somewhere in West Africa, so it had to be crank started for a couple of months until it mysteriously started working again in Malawi.

Parts are cheap, though.

 

[StevieB]

Check out its replacement though - bet parts are not so cheap for this one:

https://www.autocar.co.uk/car-news/new- ... adier-2021

 

[Mike G]

Hmmm........

 

[SamQ aka Ah! Q!]

Mike, in your paean of pain re Landies, you forgot: twin fuel tanks under the seats, usually with ill-fitting screw caps, so they confuzzle you with fumes, then catch the unwary smokers...lights that don't, clutches that catch fire ( yes, they do! ) bonnet latches that fail and 'flip the lid up' just as you start a precipitous descent, gear boxes and 2/4 wheel drive selectors that are a lottery and heaters that are just a label. I also drove an ambulance version from Browndown to Stranraer once and she rolled like a sick whale at every gust of crosswind. Shap Fell was VERY interesting...Oop Narth here, I note Ford and Nissan dominate the farmers'choice.

Sam