Building a wooden deck over a concrete one

 by David Catriel
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So we've had this very sturdy but extremely plain looking concrete porch in the back of the house, and we've always wanted to make it warmer and more inviting. The obvious solution, to us, was to replace it with a wooden one. Wood is by far warmer and better looking than concrete, and if you maintain it properly it can easily last a couple of decades before you need to start replacing a piece here or there. On the downside, obviously, is the commitment to maintain it regularly. And by regularly, I mean a thorough cleaning and restaining (or repainting) once every two or three years.

Replacing the concrete deck with wood could have been done in one of two ways: completely demolish the concrete porch and build a 100% wooden one in its place, or use the concrete as a base and just add wood on top of it. Since our concrete was in good condition and would offer a solid base we decided to keep it and just cover it all with wood. 

Building a wooden deck this way does offer the advantage of not needing to worry about digging foundations, putting in joists, etc, but you do have to worry about the proper slope of the concrete porch, allowing for good water drainage, ensuring any parts that would be subjected to possible water pooling are treated against it, and such. I've done my best to protect against those things and take notes/photos of them, but I'm sure there's always room for improvement. If you're going to build something like this, remember this really important rule: an extra ten minutes spent putting in better water protection at this point will save you from headaches, hours of hours and $$$ in replacement materials down the road.
 
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Step 1: Materials, tools, etc

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The material should be pretty obvious - wood. And plenty of it. When you go buy your supplies, make sure you get at least 10-15% extra of everything, because some beams will have unsightly knots, will not be perfectly straight (even straight ones might warp a bit in the sun if left unused for a few days), etc. Same thing applies to screws - get a lot of them.

Protection
This one comes before anything else. I've gotten dust in my eyes more times than I care to count, and have felt my ears ringing more than once after drilling and cutting. I don't want to deal with that any more, and want to avoid any damage. You should be very concerned with this as well, so make sure you use a good pair of goggles that seal the space between the lenses and your skin, as well as good ear plugs. Do yourself a favor and get a pair that can be easily removed and put back on (like the pair in the photo) even if your hands are dirty, as you'll need to do this often.

Wood  
Depending on where you live and what is available, you'll probably have a choice between treated yellow pine (the green stuff) and cedar. The latter is naturally water and bug resistant, smells awesome and looks great as-is. The former is three to four times cheaper. You do the math.

Treated pine can always be stained and painted any color you like, but make sure you follow the stain/paint instructions carefully. I'm staining our deck, and the instructions I found were that you basically cannot apply any stain for several months because the chemicals injected into the wood will not let the stain penetrate too deeply and this means it won't last long. I'm going to let the wood weather until next summer, at which point I'll apply wood brightener/cleaner to it and then the stain.

You also have the choice of going with composite decking materials which look like wood but are made of much more weather resistant materials. These will cost you even more than cedar but will last way longer. Their down side, though, is that they really don't feel like wood (in my opinion). You don't get the same feeling of warmth, the slight creaking, the color, etc.

Quantities - this one will depend strictly on what design you choose for the flooring, the railing and any extras like storage under the deck, benches, etc. I've used the most common sizes of available lumber, though:
2" x 2" and 1" x 2" - floor support, railing balusters
5/4" x 6" x 10' - floor boards, railing top caps
2" x 6" x 10' - skirts
4" x 4" - railing posts
2" x 4" - top and bottom railings

Screws and bolts
There are a whole bunch of screws you can use on lumber, but you must absolutely ensure the ones you get are meant for use with decking (i.e. weather and [if using treated wood] ACQ resistant). The chemicals in treated wood will interact with non ACQ-approved screws and cause them to corrode (due to high levels of copper in the preservative), so you want to avoid that. 

Sizes - most of the screws I used were 2" long, as that would go through the boards and offer a good amount of catch onto the base beneath them. For the handrails I used 2" screws (and nails) for the balusters and 3" screws to attach the railings to the 4" x 4" posts.

You'll also need concrete screws (e.g. Tapcon) for attaching the floor supports to the concrete. I used 3" screws for this step.

Finally, for the railing posts, you'll need 0.5" x 6" (for notched posts) and 0.5" x 7" bolts (for non notched posts) to attach the railings to the sides of the porch. The concrete in my case is 6" thick, which is enough room to attach to bolts one on top of the other, about 2" apart. If yours is any thinner I'd suggest looking for alternatives.

Nails  
I used 4" nails to attach the balusters to the railings (along with the 2" screws). Same rules applies as for the screws - get ACQ approved (perhaps even galvanized would work)  nails.

Glue
I used a fair amount of construction adhesive for places like the floor support, the skirts and the balusters, so you'll need several tubes of it. I also used carpenters glue when gluing the supports for the benches, but could have used the construction adhesive there as well. 

Silicone
Anywhere the water has a chance of accumulating near wood should get extra attention, and the first place this happens is on the concrete next to the runners. The wood is already treated against water, but since these places will be inaccessible in the future you want to do as much as possible now to prevent water damage later on.
 
Wood sealer
Treated wood is basically wood into which a preservative liquid has been inserted by using a vacuum and lots of pressure. It's important to note, though, that this preservative does not make it all the way to the core of the lumber, and only infuses the first inch or so on all sids. This is just fine if you'll be using the lumber as-is, but you won't. You'll be making a ton of cuts to fit the wood into different sizes and shapes, and will be exposing the untreated innards to the elements. To protect these areas against moisture and bugs you'll need to treat them with a wood sealer, which is basically a liquid that smells a bit like paint thinner. It is transparent and does not leave a trace (you'll see it for the first couple of days but nothing afterwards), and can just be brushed on to the freshly cut ends. Keep this stuff nearby as you'll be using it often.

Tools
 I most certainly don't envy people who had to build stuff before the advent of power tools. Even with the following ones you'll still need a bit of strength for some of the steps. 

A regular drill and a hammer drill - You'll be needing two drills throughout the whole process because the vast majority of the holes will have to pre-drilled before putting screws in them. You'll also be needing a hammer drill for the sections where screwing into the concrete are concerned, so I had a regular drill with a screw head on it, and the hammer drill with either the masonry bit or wood bit on it depending on what step I was on. You don't need the drill to hammer when drilling pilot holes in wood, so a hammer drill that can turn the hammering action off is preferable.

Saws - you'll need a regular handsaw (for finishing cuts), circular saw, miter saw and a reciprocating saw. The last one is optional, though. I thought it would be a help in trimming the posts to their final height but could have just done it with a circular and hand saw.

Usual toolbox of stuff - hammer, screwdrivers, level, chisel, etc.

You'll also need wood drill bits, as all screws should be going into pilot holes instead of into raw wood. Using pilot holes on everything will certainly take you longer, but will avoid cracking and reduce the stress on the wood helping it last longer.
Vince_33 says: Jan 21, 2012. 5:49 AM
I really enjoyed reading this - it's given me lots of ideas. Thank you very much for taking the trouble to post such a detailed description - much appreciated!
David Catriel (author) in reply to Vince_33Jan 21, 2012. 9:06 AM
Glad you enjoyed it, and thx for taking the time to say so. The comments are appreciated by the authors as much as the articles are appreciated by the readers :)
captain Jack says: Jun 22, 2012. 2:29 PM
Beautiful! Well thought out. I especially appreciate the detail you provided on the railing construction. Well done.
David Catriel (author) in reply to captain JackJun 22, 2012. 4:13 PM
Glad you liked it, and thx for the compliment.
colelemi says: Mar 7, 2013. 7:40 PM
I've seen decks in Cambridge like this, but didn't know how to go about building it. Thanks for posting!
David Catriel (author) in reply to colelemiMar 8, 2013. 3:31 AM
thx. hope it helps you make your own :)
drawe21 says: Nov 29, 2011. 2:32 PM
I like it, I would make the box's around the edge taller to top of fence for planters with storage access under planters on the front. (6 to 12 inchs of dirt at top) I love storage.
David Catriel (author) in reply to drawe21Nov 29, 2011. 3:07 PM
Not a bad idea. The boxes are already used for storage, but were left at half the height of the railings so people have a place to sit.
tim_n says: Oct 7, 2011. 3:10 AM
I've got a large flat slab outside my house, but it has cracks and doesn't drain water away very efficiently, so I'm currently considering my options - one is to cover in decking, the other is to lay a concrete patio over it.

I was interested to see how you deal with the wood sitting on concrete - and I see what you've done - just laid it on top - as the concrete is porous, surely the water will seep under the silcone and work its way into the wood? I've been recommended when I put a shed on concrete pavers to put off cuts of pond liner or similar to stop the water soaking up into the wood.

Similarly depending on the variation in temps, won't the sealant eventually split off?

It's a neat job btw... just curious to what you think!
drawe21 in reply to tim_nNov 29, 2011. 2:34 PM
Clean out the cracks as deep as you can and Epoxy them closed, then you can hide the ugly fix with this wood project.
David Catriel (author) in reply to tim_nOct 7, 2011. 5:03 AM
Several considerations here. First off - yeah, concrete is a bit porous, but the kind used for exeterior construction is usually a bit better at repelling water since it's exposed to it all the time. No telling if any additives were added to the mixture when it was made, but I have to trust that it was done properly.

That being said, it's always possible that some water will get through to the wood, but sealing the edges between the wood and the concrete should minimize that.

And as for climate changes affecting the sealant - also, a possiblity, which is why I used high grade exterior use sealant. Should buy me a few more years. We've got a lot of heat, water, snow and ice over here, so it will definitely be subjected to the elements.

Finally, you have the fact that the wood is treated lumber, and has been attached at several points to the concrete. Even if some part of it starts weakening, I have faith that the wood (as a whole) will stay solid and well attached for years to come.
daveand5 says: Oct 31, 2011. 9:53 AM
Nice looking deck, and an improvement, but....
ACQ is protected against insects and fungi, not moisture, proper drainage does that. Just do a search for ACQ and read the facts.
Standard building code calls for 16" centers not 18"
Proper drainage starts with the side of the house, proper flashing to redirect the water away from it and the deck. Proper flashing and rubber seals make a deck outlast the home.
"skirting" should be applied to cover the ends of the decking for esthetic reasons and with proper drainage with flashing to protect the wood joists.
A spot of glue on each runner where the decking touches extends life of the wood and 'firms' up the deck tremendously. also eliminates screws from backing out from vibration.
I use the 20yr siding stain on the decks I build, since most 'deck stains' say right on the can, to reapply yearly, clearly a rip off.
Always check with local authorities on building codes and accepted practices to avoid fines and rebuilding.
Again nice deck, and enjoy a bbq and beer on a warm evening for me.
David Catriel (author) in reply to daveand5Oct 31, 2011. 10:22 AM
Thx for the info. Drainage won't be a prob since the concrete is already slanted away from the house, and we'll be treating/staining the wood next year for extra protection and looks.
jblanton1 says: Oct 6, 2011. 3:41 PM
Since your concrete was in good shape, I would have just covered the concrete with slate or some other stone instead of wood. With a concrete deck, you had something that was basically maintenance free -- basically you just pressure wash it when it gets too green for your tastes. With wood, you're going to be pressure washing, resealing, replacing rotten boards, fixing loose boards, etc from now on. I've owned houses with wooden and concrete decks / patios before and in my opinion, the concrete is a better choice.
David Catriel (author) in reply to jblanton1Oct 7, 2011. 5:04 AM
A wood deck will defintiely take more work in maintenance that concrete, and I think I mentioned that somewhere in the article. It all comes down to what your tastes are, and in my opinion nothing beats the warmth and aesthetic value that wood has. It's well worth the maintenance costs.
Azayles says: Oct 6, 2011. 8:09 AM
Norm Abram himself would be proud!
This is a fantastic instructable, very detailed and well put together.
sfurst in reply to AzaylesOct 6, 2011. 10:41 AM
AHH . . . Norm Abrams. I was already getting all sentimental thinking about my dad today (he's been deceased 12 1/2 years) and then I see this AND the Norm comment. My dad LOVED Norm Abrams, the New Yankee Workshop, This Old House, etc. He always joked that "Normby" was on . . . "Time to watch Norm-by!" I actually got to meet him in 2001. The man has a router for every bit he owns so he never has to change a bit. THAT is woodworking luxury!

That being said, my dad (an accomplished woodworker) would be impressed by your work. Wanna swing over to Wisconsin and build one for me? ;) Great stuff.
Azayles in reply to sfurstOct 6, 2011. 12:08 PM
Wow, I didn't know he had a router for every bit! Mind you, the size of his workshop and the stuff he used to turn out :P Not really surprising!
Also the safety glasses. very important that.
"There is no more important safety rule than to wear these safety glasses"
Wise words indeed.
David Catriel (author) in reply to AzaylesOct 6, 2011. 1:41 PM
I would add the ear plugs to that ...
rgerber1 in reply to AzaylesOct 6, 2011. 1:01 PM
I heard an interview with Norm,, I also remember the very first "This Old House" show, Norm actually was just a hired carpenter for the job along with several others. The Construction lead never showed up and the camera's were rolling. Bob Villa saw Norm walking by with a ladder and stopped him and started asking him questions about the job..

Norm was one lucky SOB,, that made his future.
David Catriel (author) in reply to sfurstOct 6, 2011. 11:31 AM
That's got to be one of the most flattering comments I've received to date. But in spite of that, I've got to turn Wisconsin down. Trust me - the paperwork my wife would have you do in order to borrow me for this project just wouldn't be worth it!
David Catriel (author) in reply to AzaylesOct 6, 2011. 8:34 AM
Never knew who Norm Abram until this comment (and Wikipedia) came along. Thx for the learning experience :)
Azayles in reply to David CatrielOct 6, 2011. 9:14 AM
I used to watch his New Yankee Workshop show all the time when it aired in the UK. Well worth looking out for his work if you're into the carpentry :-)
jzelensk says: Oct 6, 2011. 9:21 AM
Really well-done project and photos. Congratulations!
David Catriel (author) in reply to jzelenskOct 6, 2011. 10:26 AM
Glad you enjoyed it.
Ortzinator says: Oct 6, 2011. 8:23 AM
That concrete looked terrible, good job! The roof is next perhaps? :o)
David Catriel (author) in reply to OrtzinatorOct 6, 2011. 8:35 AM
Thx. Would love to redo the roof, but I think I know a non-one-man job when I see one. The shingles need some TLC all over the place. Time to call in the experts and have the whole thing redone ...

Then again, maybe I can cover it in treated wood to match the deck? I wonder what the wife would to that.
derte84 says: Oct 6, 2011. 6:32 AM
nice and simple!
David Catriel (author) in reply to derte84Oct 6, 2011. 6:46 AM
Hi
Thx for the comment. I wouldn't exactly say the project was simple to make (although you're probably referring to the design), but I agree that it was nice :)
buckmcf says: Oct 3, 2011. 12:27 AM
Exactly what I was thinking of doing to my back patio.
David Catriel (author) in reply to buckmcfOct 3, 2011. 3:55 AM
Then go for it. It's a bit of work, but so worth it in the end.
Sermos says: Oct 1, 2011. 11:19 PM
Nice! Definitely makes the house look more inviting.
David Catriel (author) in reply to SermosOct 2, 2011. 4:50 AM
Thx. Yeah, makes a huge difference over concrete.
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