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Converting Carport to Garage

InspectorRandy's picture

Need to convert a carport to a normal garage.

The carport is supported by four 4x4 posts carrying 4x10 beams and truss framing. The posts are supported with metal saddles projecting above the slab--the type with the 1" steel rod to lift the saddles off the concrete. The thing has been there for 50 years so structural support isn't an issue.

The carport is attached to and integrated with the home and roof. 

I plan on "in-filling" the exterior walls using typical 2x6 framing, 7/16" ply sheathing and siding to match.

One concern: if I set the walls directly on the slab, there won't be any clearance from the bottom of the siding to the concrete so water can drain.

One idea is to pour a small 6"x6" curb to mimic a foundation stem wall so the wall sill can sit off the concrete.

The other idea is to cut the slab flush with the exterior wall surface so there will be a clearance from the bottom of the siding.

Which one wouldl you do?

Any one converted a carport before and want to add anything I'm not thinking about?  

Definitely don't put wood (post #215381, reply #1 of 9)

Definitely don't put wood sills directly on the concrete floor, regardless of siding issues.  Probably you should pour (or construct from blocks) the curb you describe, then be sure to use a waterproof spacer between that and the sill plate of the wall.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Hi there, I have done a few (post #215381, reply #2 of 9)

Hi there, I have done a few of these carport to garage transformations.  They are very straightforward usually.  If the posts are 4x4s, then you probaby don't want to use 2x6 for the wall frames unless you plan to insulate and finish the interior.  If the slab is more or less dry and totally above grade then a treated 2x4 sill can be installed between the posts, then the walls are framed conventionally.  You can use treated ply to sheathe the bottom 2 feet of wall or use regular CDX and wrap the bottom edge with Ice and Watershield before it is installed.  With either sheet material, you should install the Ice and Watershield up 2 feet or so.  Then install a PVC watertable down to the slab.  If the exterior wall plane allows, it is a better detail to run the PVC trim past the top of the slab to close the joint between the slab edge and sill.  After the watertable trim is in, you can install really any siding you like, provided you are at least 8" above grade with wood.  I don't recommend pouring new concrete on top of old or building a masonry curb.  It will be more work, harder to waterproof the joint and not look any better in my opinion.  I attached a quick sketch to show you how we typically do this work.  Good luck.  

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Has anyone considered using (post #215381, reply #3 of 9)

Has anyone considered using cement board for the bottom rip of sheathing in an installation like this? The cement board could be covered in stucco or veneer masonry to mimic a foundation wall.

I have used tile-backer style (post #215381, reply #4 of 9)

I have used tile-backer style cement board to replace fiberboard sheathing in locations where splashing caused the sheathing to deteriorate.  Not really a fix for sheating that reaches the carport deck, however.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Why wouldn't it be a fix for (post #215381, reply #5 of 9)

Why wouldn't it be a fix for sheathing that reaches the carport deck? Seems to me it would work nicely. Use some kickout flashing between the cement board and the regular sheathing. Maybe some liquid membrane or peel and stick ice and watershield over the sheathing and onto the edge of slab so that you dont get water under the sill. Should dry out nicely if it gets wet and solves a host of problems...

If the cement board sits on (post #215381, reply #6 of 9)

If the cement board sits on the slab it will absorb water, transmitting that up into the framing.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Thanks for the feedback and (post #215381, reply #7 of 9)

Thanks for the feedback and ideas so far.

I like the idea of dropping the wall sill all the way to the slab rather than builidng a poured concrete or concrete bloack curb, but the slab extends beyond the plane of the exterior wall surface about 16".  IOW, the slab edge is directly under the roof edge.

What do you think about snapping a line and cutting the slab?  Less work and less future problems than creating a concrete curb? 

If you put a plain wood sill (post #215381, reply #9 of 9)

If you put a plain wood sill on the slab (anywhere but perhaps in Arizona) it will rot out in fairly short order.  For your situation the sill, if directly on the slab, should probably be "ground contact" treated lumber, and it wouldn't be silly to put a second layer of treated atop that.  Having the slab stick out 16" makes it worse, but it's still pretty bad regardless.


Of all the preposterous assumptions of humanity over humanity, nothing exceeds most of the criticisms made on the habits of the poor by the well-housed, well-warmed, and well-fed.  --Herman Melville

Thanks for the feedback and (post #215381, reply #8 of 9)

Thanks for the feedback and ideas so far.

I like the idea of dropping the wall sill all the way to the slab rather than builidng a poured concrete or concrete bloack curb, but the slab extends beyond the plane of the exterior wall surface about 16".  IOW, the slab edge is directly under the roof edge.

What do you think about snapping a line and cutting the slab?  Less work and less future problems than creating a concrete curb?