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/ Structural engineers out there...

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Ed Booth - on 16 Apr 2018

Hi, I'm looking at the feasabilty of converting a garage with conventional pitched roof into home climbing wall.

Most garages I see on the houses we've been looking at have got ceiling height tie beams, and also sometimes zig zag or squared additional beams in the void. What is the feasibility of placing one support beam on the inside of the ridge or even just some high tie beams and removing the rest to give a space high enough for a wall .

p.s I'm aware I would likely need to get an engineer to give advice on the specifics, i'm just trying to get a feeler.

Cheers, Ed

Post edited at 08:17
Ally Smith on 16 Apr 2018
In reply to Ed Booth:

I await replies with baited breath - I have similar plans for my new house too!

jkarran - on 16 Apr 2018
In reply to Ed Booth:

I'd have a look at how loft conversions are done in buildings with trussed roofs to get an idea what's possible but ultimately you'll probably need an engineer. I'd assume the rafters aren't stiff enough to adequately support the roof load with the truss work/webs removed even if you can stop the walls spreading so there'd be a fair amount of work/material required to increase their stiffness provide additional support from the gable walls before you can move the ties up or add structure elsewhere to completely replace them.

Presumably the two options for making more space in a garage are to redesign the trusses to create a pitched ceiling or convert the roof to a more traditional structure with the addition of stout purlins and wall plates tied together at the ends.

jk (not a structural engineer)

Eric9Points - on 16 Apr 2018
In reply to Ed Booth:

My guess would be that you'd have to remove most if not all of the roof and rebuild it. The tie beams are there for a reason.

Best show it to a structural engineer.

krikoman - on 16 Apr 2018
In reply to Ed Booth:

It'll be fine, just chop out anything that seems to be in the way.

 

(Not a structural engineer, either)

mkean - on 16 Apr 2018
In reply to krikoman:

This is the easiest way of finding out if a beam is in tension or compression:

- If it goes twang just before you finish cutting through it is in tension. 

- If the saw binds up half way through it is in compression. 

- If you are part way through and it snaps, swings round and smacks you in the face then the whole lot was on the skew in the first place. 

More seriously this is definitely a job for a structural engineer, which I am not. If you take out the beams in tension then the roof is going to attempt to splay out, is there an option to put in a ring beam at the top of the wall? (I realise this is likely to be costly).

Pina - on 16 Apr 2018
In reply to Ed Booth:

In short, the tie beams are there to work in tension so you'd need to have an equivalent system in place to take up the loads. As mentioned by Eric, it would possibly mean rebuilding the roof or building up a truss system to redistribute the loads to an adjacent beefed up tie beam (hard to tell without seeing the current system in place).

Changes like that would need to be signed off by a council engineer so I'd consult with a local firm to get through the process. (I think, don't actually deal in residential).

As a side note, any free advice given by a structural engineer for a conversion like this could be regarded as a contract under English law and any issues would make them professionally liable so anyone who doesn't have personally liability insurance (myself included) would tread carefully with regards to dishing out advice

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Rigid Raider - on 16 Apr 2018
In reply to Ed Booth:

Creating a void in a modern attic, which is full of trusses, is an expensive business. To support the weight of the roof you will need at least two full-length steel I beams inserted into the roof through a hole in one gable, meaning you will end up with something like the beams you see halfway up the sloping ceilings in older houses. In addition you will need tie beams or rods at floor level to prevent the roof from splaying outwards. 

MikeYouCanClimb - on 16 Apr 2018
In reply to Ed Booth:

You could look at your project another way

 Instead of asking suppliers, builders etc what you really want in the first instance, ask the question differently, for example, “I want a wide velux window” (I think up to 1.4m width may be possible).

 Doubling or tripling trusses before removing intermediate ones is one solution my builder suggested.

 Mike

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elliott92 - on 16 Apr 2018
In reply to Ed Booth:

to cut it short.. it is not a feasible idea. if it were a traditionally pitched roof then no problem.. you could put a small steel or flitch beam under the ridge and run some high collars through to create triangulation (everything in a roof is about transferring weight through and tying the building together with triangulation and positive connection). cutting out trusswork is a different ball game as a few people have said, truss timbers are much smaller in size and are not designed to take load through just the rafters, it all transfers through to the ceiling joists too (note how your cross members all form triangles..). what you have to think about is mass weight gain under snow load, which could end up cracking those little 4" x 2" truss timbers. when i do loft conversions on truss roofs its a nightmare, we use a very expensive design and product called telebeams, but even this wont give you the skiing ceiling effect you want. in my opinion your best bet would be to strip and traditionally recut the roof. Elliott (first fix carpenter and loft converter specialising in very complicated cut roofs) (and someone who works in the real world, not the structural engineers 10x overstated calcs)

Steve Clark - on 16 Apr 2018
In reply to Ed Booth:

If you want to remove ALL the timber at ceiling joist / bottom chord / wall plate level, then you are as well to re-build the roof. Ridge beam or a couple of (probably) steel purlins. Strip the lot and put it back together. You will be able to reuse a lot of battens & tiles etc.

If you just want to remove a number of joists / bottom chords to fit a moon-board or similar, say 8ft wide, then you can probably do it internally. Effectively build a stronger truss either side of the gap and fit short purlins to carry the intermediate rafters. Then chop out the bit you need and build the wall.

If you’re smart with it, an alternative is to use the climbing wall structure itself to support the roof. A clever sequence of install and cut-out. Effectively a big triangular truss taking load directly to the floor. You could end up with England’s strongest garage roof, but it does limit your flexibility in use of the space in the future. 

You need the right kind of engineer. A design & build structural engineer with temporary works experience or a timber frame designer.

Post edited at 18:43
Ed Booth - on 16 Apr 2018
In reply to Steve Clark:

cheers, Thats all the kind of answers i was expecting. My concern with rebuilding is that the roof concerned, is a double length section of garage that is part of the building of the neighbours garage also and it is one continuous roof. I don't know enough about it all to know if its easy enough to take all the tiles off my bit and get a new steel structure inside and then put the tiles back on so it looks and connects exactly the same with the neighbours part without pissing them off.

Thanks, Ed

Misha - on 16 Apr 2018
In reply to Ed Booth:

You want to get even stronger or thinking about getting the offspring started early?

becauseitsthere - on 16 Apr 2018
In reply to Ed Booth:

Is it really worth that effort for the additional space. 

I went for a completely horizontal roof the full length of the garage. Independently supported on the side panels. 

Ed Booth - on 17 Apr 2018
In reply to becauseitsthere:

i think it is . I worry a horizontal roof isn’t that reflective of most climbing I will do. I think when it gets to circuits etc the height really does make a difference. Just my opinion tho. I know plenty of people are happy with a standard ceiling height wall and horizontal section. Thanks Ed 

 

French Erick - on 17 Apr 2018
In reply to Ed Booth:

Steel's gonna be financially steep...not the steep you had in mind!

Ed Booth - on 17 Apr 2018
In reply to French Erick:

How much ball park roughcost would you say for steel? 

David Coley - on 17 Apr 2018
In reply to Ed Booth:

Do you have a large garden? If so, it might be a lot easier to build a free standing structure. Mine is amount 16ft by 12ft in plan, two over hanging walls at different angles. 3k including holds.

See my profile picture.

 

AJM79 - on 17 Apr 2018
In reply to Ed Booth:

Strip the lot and re-build as a traditional rafter and purlin roof, I'm afraid.

Oversize your rafters to compensate for the extra weight (boards and people).

An engineer may find a way around this but it is likely to be costly and complicated.

I'm not a structural engineer but I am a builder and trusses are not designed for being cut out.

Good luck with it, and steel's really not that expensive compared to the full re-roof 

French Erick - on 17 Apr 2018
In reply to Ed Booth:

I wouldn't dream to give you a figure as my knowledge is 2nd hand at best (dad and brother are blacksmith/steel workers- they do warehouses, ramps, stairs...), and also I have no idea of the size of your garage! All I know is that steel is not cheap. If you have to assemble it, you need someone to cut it and weld it (plates with holes so it can be bolted). That demands specialist equipment + means of transport) and thus comes at a premium.

As someone suggested before, is there room for you to build something purpose built? I did so in my garden and kept the garage as my workshop!

Steve Perry - on 18 Apr 2018
In reply to Ed Booth:

Build some gothic flying buttresses down the outside of your garage and turn it into the cathedral of climbing.

Post edited at 00:11
jkarran - on 18 Apr 2018
In reply to Ed Booth:

It seems to me people are being rather pessimistic about your options. The trusswork serves two functions, to stiffen the rafters and to stop the roof spreading, flattening out. Both functions can be replicated with other structures. The rafters either side of the triangulation nodes are evidently stiff enough already to carry the roof, if the support provided by those nodes can replaced with purlins then you're left with tying it all together so the horizontals can come out. There you have several options depending on the shape of the space you ultimately need. All that can potentially go in from below (or worst case through the gable wall) before the trusswork comes out. I'd get an engineer in to have a look, see what they think. It's not going to be especially cheap but if it's important to you it's not likely to be technically impossible either and it may still be cheaper than a new roof.

jk

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Ally Smith on 20 Apr 2018
In reply to Ed Booth:

Ed - did you consider the other option - can you dig down, reseal the floor, and thus make enough headroom for a decent height board?

Ed Booth - on 20 Apr 2018
In reply to Ally Smith:

Not really thought about that one but I would certainly mention it to the structural engineer as an option.

Are you in the same boat then?

It seems so ridiculous when they make trusses that they don't consider the needs of the modern day climber :-p

Ally Smith on 20 Apr 2018
In reply to Ed Booth:

I've got an offer accepted on a house with detached garage with pitched roof.

Currently the joists are hidden by chipboard flooring, making a small loft space, so i'm not sure exactly as to the suitability of making it into something taller.

Ideally i'll find enough room for 3.15m worth of Moonboard Maybe with an extra panel to the side for downclimbing/circuits though if there are joists poking through this bit then i'm not fussed.

 

john arran - on 20 Apr 2018
In reply to Ed Booth:

I'm no structural engineer but if the only load on the roof is the roof itself I find it hard to believe you couldn't at least remove a portion of the beams and replace the support they provided by joists across the beams that will still be in place. Like when you cut a floor hole for a staircase and you just cut a couple of floor joists and tie the loose ends across to the remaining joists on either side of the hole.

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Eugetj - on 20 Apr 2018
In reply to Ed Booth:

Simple notes from a structural engineer who designs climbing walls and buildings.

Garage roof  - formed using timber trussed rafters (at approx 600 c/cs) - these have internal diagonal members and a ceiling tie and the timbers are circa 38/44 mm wide. These are designed as a single unit all members contribute to the ability of the roof to stand up. Don't cut the members unless a design has been done by a  structural engineer which will probably involve the insertion of steel or possibly timber purlins at strategic points under the sloping members.

Garage roof  - formed using timber rafters with a  ceiling tie, no internal members. The rafters (sloping members) prop each other at the ridge and therefore there is an outward thrust imposed to the top of the walls at the point the rafter is supported by the wall. The horizontal ceiling tie will normally be fixed to the rafters, this stops the outward movement and is in tension. Don't simply cut this away. It is possible to design a ply diaphragm added to the rafters either on their top or to their underside to take the thrust back tot eh ends of the garage where a tie can be fixed to carry all the thrust out. This does need to be designed properly.

 

 

Rick Graham on 20 Apr 2018
In reply to john arran:

> I'm no structural engineer but if the only load on the roof is the roof itself I find it hard to believe you couldn't at least remove a portion of the beams and replace the support they provided by joists across the beams that will still be in place. Like when you cut a floor hole for a staircase and you just cut a couple of floor joists and tie the loose ends across to the remaining joists on either side of the hole.

What I do not think you appreciate , John, is the difference between a truss and a beam.

Some elements of the truss are in tension, some compression and depending on the rigidity of the joints some bending and shear.

The OP has referred to tie beams at ceiling height.

Take these away and the walls are pushed outwards

gilesf - on 20 Apr 2018

Even if you do the majority of the work yourself it's going to cost a lot. In the event you decide to go ahead then paying a professional to look at it and come up with the calculations is an absolute necessity.

Cutting trusses out and trimming in order to create the space you need is NOT the way forward.

john arran - on 20 Apr 2018
In reply to Rick Graham:

You're right that I know very little about this, but my version of common sense would suggest that, regardless of the direction of force, a sufficiently robust bracing member along the base of the roof, secured to other tie beams that will remain in place, should be able itself to be secured to the walls and provide the required level of support. Unless, of course, the existing structure is barely strong enough already.

That was my layman's point anyway. I'm sure the OP will (and certainly should!) pay more heed to knowledgeable experts, but it would certainly be worth raising with such experts the idea of removing only as much of the supporting structure as is really necessary (and bracing as required to compensate) as opposed to replacing the whole lot with a different mechanism.

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