Flat Top Roof/Deck

[avewhtboy]

Hi first post, trying to figure out design for a garage in my back yard.

My concern is wanting 13 foot ceilings for car lift requirements without having a really tall roof line.

So what I was thinking was just having a flat or slightly sloped roof to keep overall height down.

Then I got to thinking, why not make that a use able outdoor space, aka roof top deck. It would seem feasable using metal roof trusses or even floor trusses with proper bracing design.

I searched here but really didn't find anything like this.

If there are relevant threads please let me know.

thanks

 

[James-W]

Personally, I would not recommend a flat roof. I know there are a lot of flat roofs out there, and if they are done correctly they are fine. But I really think you would be better off with a traditional roof rather than a flat roof. You can get trusses made specifically to give you more "floor to ceiling" height, and that would be my suggestion to you.

 

[volleyball]

What you want is aluminum decking. The kind used for docks. There are a few companies that make the product. It ain't cheap. I have 18' depth with about an inch and half pitch.
The decking is waterproof so it will be your roof and deck flooring in one which reduces cost.

 

[kbs2244]

Check out the local industrial park builder.

Around the Chicago area the typical building is 50 feet wide x 100 feet long.
There is an 8 inch slope from one side to the other for the roof drainage.
They set the roof trusses one block higher on one side of the building.
Roofs are traditional tar and gravel or rubber membrane.

In one industrial park near an outdoor theater roof top use is common.
Now that the theaters broadcast on low power FM you can sit outside the fence and listen with no problems.

 

[kd3pc]

flat roofs, unless commercial quality and installed can be a pain for the homeowner. Flat roofs keep more snow, require slope to drains and someway to keep debris off. More expensive to install than conventional roofs.

WHile the idea of building a deck or dock above is great, the reality and legal requirements for safety will likely be even more of a pain.

Location will play a parts, as regards snow....so you will need to factor that in. But it can be a solution to a strict zoning requirement.

 

[ADSR]

I love flat roofs. No wasted space just for looks.

 

[glider]

What you want is aluminum decking. The kind used for docks. There are a few companies that make the product. It ain't cheap. I have 18' depth with about an inch and half pitch.
The decking is waterproof so it will be your roof and deck flooring in one which reduces cost.

I love the idea. I think we need some pics.

 

[volleyball]

Lockdry, the stuff I used.

 

[Lippyp]

A friend of mine up in Lancashire built a half underground garage, his house is on a steep hillside on a level area carved out. He excavated another flat area and built a concrete box basically, fully waterproofed like a basement and then backfilled around it and he now uses the top as a deck/garden. I know at one point he was talking about covering it with fake grass. It looks like Thunderbird 2 should come trundling out of it! I believe the roof is beam and block with a concrete slab poured on top.

 

[avewhtboy]

Thanks for the replies and info.

I live in Atlanta so Snow is not much of a factor though rain is!

The boat dock decking sounds like a good idea and should be readily available around here so I may look into that.

Mostly I was wonder what type of roof joists to use. I was thinking either Steel or wood floor trusses for the roof?

I am thinking I will build 30x30 space.

 

[volleyball]

My area is a quarter of that so some lvl's and PT lumber did it for me. And it has held feet of snow without bowing. Nothing under it has ever gotten wet.
I would think steel would be best because people are heavy. You don't want a collapse.
Remember you install this as a porch, not a deck.

 

[wssix99]

I searched here but really didn't find anything like this.

I just built a house with the main roof and deck over the garage flat.

Flat roofs can be a nightmare, but can perform better than a sloped roof if you do them right. (You can get some flat roofs with a 100 year warranty.)

Are you going to do the work yourself?

Depending on the size of your garage, wood floor trusses will be the easiest and most cost effective to install. Again, depending on the size/strength of your roof, the trusses will add extra depth to your ceiling. In my case, they span 28' and are 2' high.

One key is reducing penetrations. That is a common point of failure. For our house, we have zero roof penetrations and a welded roof membrane. As long as we don't puncture the membrane, there's no way water can get in.

A quality membrane coating will cost a little more, and so will the higher quality underlayment you'll need if you are going to use the roof as a deck.

 

[ilovevocs]

Their are a myriad of Manufactuers and system configurations that would suit your needs with NDL warranty terms up to 30 years. You likely will not get such a warranty in a residential application but the system can be installed per Manufactuers specifications for that warranty term and be service free if it's installed by a quality contractor. Tell my your SF and your budget and I'll give you some guidance. My dad is a commercial roofing contractor, I'm an architect by education, and after practicing for a while I returned back to roofing. The structure will have to be designed to handle the overburden. Options for the walkable surface are wide open but they all have an impact on cost and easer of service/ leak detection. At one point a few years ago I installed the largest vegetated roof system in the state. Sure that no longer holds true as it's becoming more popular. Not trying to tout my expertise, just saying I know my stuff and I can provide allot of guidance in product selection, system configuration and detailing.

 

[Apex Structures]

Go for the design you like, flat roofs that are installed properly will not cause any problems.

 

[RickP]

The type of ceiling joists you choose depends on the span and whether you have posts down the center of the garage. Wood joists would be the easiest way to go if you have posts and a beam down the center. Otherwise, you could use engineered lumber or steel, but I think the LVL/PSL type wood beams would be cheaper than the steel. I have three flat roof decks on my house and they're all supported by wood joists, but my spans aren't as big as yours.

For the deck surface, are you planning to use it as a traditional deck, with furniture, etc.? If so, then the surface has to be tough enough to stand up to the furniture legs being dragged across it. The best way to do that is to build a sleeper deck on top of the flat roof, using traditional deck lumber or synthetic deck boards. Then you can make the flat roof from whatever material you want.

If you'd prefer to avoid the sleeper deck, I'd recommend a material like DuraDek - it looks like a no wax kitchen floor and has a really good system for waterproofing the edges and railing posts. Good luck!

 

[LS6 Tommy]

Grow grass on it and keep your heat gain down...

Tommy