My concrete block garage so far!

[boatbuilder]

Hi,

I've been DIY building my 20 foot x 40 foot garage way over here in Ireland.
Its cavity wall construction, made of a 4 inch inner block, 4 inch cavity and a 4 inch outer block, all held together with stainless steel wall ties.

I'm currently looking for some roofing advice so please can I have some ideas please? I need rooflights!

 

[Yotaforce]

Steel over insulation. It will last longer than asphalt singles. Color is always nice too.

 

[1320stang]

What do you put in the cavity?

 

[Namocsid]

Nice bus too! (for a baywindow)

 

[flesburg]

What beautiful countryside!!

 

[kbs2244]

My pick for the roof is sheet steel with plastic skylights.
Another thought is a band around the top of the wall glazed with plastic. You could leave out a 3 block space with a block in between each space. Your top plate would bridge the gaps. This would give you good lighting without any worry about leaks.
We do it on pole barns around here, and as long as the building isn't super deep, the light is good.

 

[boatbuilder]

The cavity will be totally filled with polystyrene beads coated in pva, blown in after construction through holes drilled in the wall.

I'm thinking of putting a steel insulated panel roof on it, as my brother works for Kingspan Panels and can get me a discount. Its basically a sandwich of insulating foam in between two sheets of corrugated steel.
It is simply screwed down to either timber or steel purlins. Kingspan also have insulated Polycarbonate rooflights that i'll use too.

I'm totally confused about how to actually frame the roof though! Do I use steel I-beams or timber rafters? Do I put an A shaped roof, or a lean-to? I'm confused, mainly because its a cavity wall which is not very strong when pushed sideways. I don't want to have the roof pushing the walls outwards, cracking them. I also need to have the interior roof space fairly free of obstruction because I want to build a boat in there at some stage! The bus is another project! Needs some new panels welded in soon, so the garage needs to get done pronto!!

 

[flesburg]

Just my 2c worth:

I would use wood trusses. The load is straight down on the walls. Very common here in the US. Trusses with 2x4s can easily span 20 feet and can be on 24" centers. With 1x4 furring strips, you can then fasten a metal roof. Pitch of roof probably should depend on your snow load. Insulation should be at the ceiling height to cut down on the cu/ft you are heating. 5/8 drywall ceiling can span 24" centers.

 

[boatbuilder]

Snow is not an issue in Ireland as we don't really get much at all.

My problem with using wooden trusses is that the roof space becomes unusable and the ceiling height under them would be too low for my purposes.
Also if I slabbed the ceiling etc, there would be no light from rooflights!

 

[kbs2244]

Go to what we call a "sissors" truss. You get some of the interior "peaked celing" effect, but at a shallower angle and not full height to the real ridge.
It more vertical interior space then with traditional joists at the level of top of the walls, but they have enough internal streangth so that they will not push the walls apart.

 

[Willy Victor]

Go with attic trusses, I have them in my pole building and I have 14X36 useable space in the attic, it's six feet high at the peak. Has a 6-12 pitch. Why is Ireland so green-cause you get a ton of rain. My Daughter-in-law is Irish. Good luck on your project.


Willy

 

[1320stang]

How about laying more courses of block? You could get trusses and have them made with a longer soffit that is stepped so the soffit is lower than the top of the wall. Another option would be to go with a Mansard roof and have the trusses designed do give you more headroom. But how will you get the boat out if it's bigger than the door opening?

 

[boatbuilder]

I've got seven rows of blocks built at the moment and I'm planning on building another five rows at least. I don't want to do any more until I have the roof design clear in my head.

Heres another idea, what do you think of it?
Would a steel gusset plate, welded at the ridge, be strong enough to stop the roof spreading?

 

[comp]

interesting build

 

[Charles (in GA)]

Given the "odd" design of the building (the cavity wall) I'd be seriously inclined to talk to a qualified engineer who could advise you on a roof type and structure construction that would not impart any side loads on the walls.

Personally I'd want thick piers of block in the wall every so often to strengthen it.

Charles

 

[boatbuilder]

Yes it is an odd form of construction, from an American point of view. In Ireland, it is actually the most common way to build houses. We've never really been into stick built structures at all, although there are some timber frame building companies here now.

I've decided to go with a simple lean-to roof, with a shallow pitch of maybe 15 or 20 degrees, so that the weight of the roof will mostly be transmitted downwards.

 

[Ironcrow]

Would a steel gusset plate, welded at the ridge, be strong enough to stop the roof spreading?

Yes. I had a house that was build this way. An engineer could do the simple calculations for you.

 

[Charles (in GA)]

Yes it is an odd form of construction, from an American point of view. In Ireland, it is actually the most common way to build houses.

Its not the block thats odd, we have lots of block construction, both structural and non-structural, its the cavity design. Here the block is (generally, or most commonly) 8 inch high, by 8 inch thick by 16 inch long and with two or three cavities in it but one solid block, seems that would be much stronger than two separate blocks spaced apart.

http://www.uvi.edu/Physics/SCI3xxWeb/Structure/BlockConstruction.html

Indeed the rest of the world builds with concrete due to the shortage of wood in many places.

The brother of my lady friend from Malaysia bought a house over here and was taken aback by the wood, he thought that was "cheap" and substandard, since only the cheapest and poorest people in Malaysia live in wooden houses.

Locally, the hardware store here in my small town just built a brand new building a block from the old store. Its large, probably 60 by 80 feet or so with 10 ft walls, and is poured concrete walls, 8" thick with clear span wooden trusses on it. Now thats solid construction.

Charles

 

[kbs2244]

Your lean to style roof will work fine. It is a common way to do 50x100 industrial park commercial buildings over here. One wall is one course of block lower then the other, so you end up with an 8 inch drop over a 50 foot span slant.
They call them a “flat roof.” Not much slope, but enough to get the rain flowing and with steel “Z” web style truss cross members there is no snow load worry.
Roof drains go through the roof on the inside of the wall and then underground to the storm drain.
You never see the roof design from the outside because they bring up what they call a brick veneer "parapet" on the outside of the block up to the same level all around the building. You have to go inside the building and count the rows of block to realize one wall is lower than the other.
I don’t know if you want to go through all that trouble. It is done for looks. A simple gutter and downspout would work fine.
You are limiting yourself to the height of your walls.
You will have to take the boat outside to step the mast.

 

[boatbuilder]

Yeah some people still use the "cavity blocks" like your picture. The downside to them is that its not so easy to insulate in the cavity...also theres a good chance that damp will seep right through the block and give you damp on your inside walls. With two totally separate walls, damp can't get through.

Luckily, I don't plan on building a boat with a sail! If I have a 9 foot high doorway, it should be fine

 

[Kevin54]

The downside to them is that its not so easy to insulate in the cavity...also theres a good chance that damp will seep right through the block and give you damp on your inside walls. With two totally separate walls, damp can't get through.

If you don't or very rarely have snow, why the need for insulation in the cavity? We have snow and it can dip down to -20F in our area in the winter and insulating the block has never really been an issue. Or at least not with most. Or 1" insulation board is put on the outside and then backfilled up to it. What is aboove ground is cut off to ground or just below ground level. Moisture problem are usually taken care of by sealing the outside with an asphalt type sealer or a rubber type of sealer.. I would also put up a scissor type truss if it was mine. And once everything is all tied in, there should not be any outward pressure on the walls. All the pressure should be downward and not outward. Backfilling will take care of part of retaining the wall on the outside, and the floor should take care of it on the inside. If anything you could always put some dividers in and add some rebar and pour concrete every so often in the void. The sill plate will tie the inner with the outer