Building a Shed under a Deck

How to build a shed under a deck. The following youtube video covers some important factors to consider when building such a deck.

I used 3dsmax to model my deck and shed.
I recently converted the 3D deck & shed plans into sketchup so that others can benefit.

Feel free to download the sketchup file and use Google Sketchup to view, measure, and modify my shed/deck plan for your own use.

FREE Google Sketchup Plans for my deck and shed.

Back in 2001 my new home needed a deck. I designed a deck that was small and simple.
The 2 posts and single beam were massive screwed and glued planks.
I am proud of the fact that I single handedly designed and built my deck.
It was a lot of fun figuring out how to lift that heavy, wet, pressure-treated beam onto the posts all by myself.
The posts weren’t small either, when you consider they are almost 6 feet underground!

Overkill should be my new middle name.

Designing my deck with only 2 posts, allowed plenty of space for a shed.
The first stage of building my shed was to build the roof within the joists of the deck.
This stage took a long time and a bunch of thought.
I decided to build an angled trough system with curved sheets of aluminum flashing.

Here you can see the underside and the gradual slope for rain runoff.

This was an incredibly tedious process. I used a large quantity of industrial caulk to seal the aluminum to the joists.
This tedium will be worth it because it maximizes my sheds headroom.
I’m 6′ 3″ and there is just 1″ of headroom from the joists.

The next time I need to cut bricks… I’ll get a diamond blade.
It sure took me a long time to cut them with an abrasive disc.

The shed roof survived the winter and showed no leaks. Now the next stage. I had a concrete pad poured. I decided to put my shed entry on the left side of the deck, so I had to dig the hillside down and create a patio for the doorway. This summer was incredibly hot and moving my sprinkler lines was no fun.

It’s took an eternity to figure out how to build the walls. I had to leave a gap between the walls and the deck. I expected the concrete to heave in the winter.

My excitement is building and I can see the light at the end of the tunnel!

The doorway is short and non-standard. I had to build a custom double door.
Another month or so would pass before I could finish my custom shed doors, but I’m happy with the result. I wanted my shed to look as nice as I could make it… so I wrapped it in matching vinyl siding. My trailer-lift project may have been my most gratifying project, but my shed has been the most useful. Good thing I allowed space for the concrete to heave in winter… because it did just that!

YAAA! My garage is clean and useable again.


  1. Andy
    March 6th, 2010 at 10:34 | #1

    Great job! I have a similar situation but my deck is not square, but has a extension towards the back of the wall and unfortunately the deck was already built before we moved in. I am thinking about modifying your roof idea so I do not have to take up deck boards. If you happen to have any plans you can send me let me know and I will provide my email. Thanks Andy

  2. Derek
    March 17th, 2010 at 08:45 | #2

    This looks great. I’m very impressed with what you came up with here.
    I’m about to start building a deck with a shed underneath it as you have done here.

    I was wondering if you wouldn’t mind sharing your plans for both the deck and the shed. My situation is pretty well the same as yours.

    Thanks, Derek

  3. March 17th, 2010 at 22:42 | #3

    OK… I converted my 3ds max 3D models into Google sketchup format and update this post.
    Go to the top of this post and you can find the link to download the sketchup file.
    Let me know if that helps!

  4. Gary Miller
    April 9th, 2010 at 14:16 | #4


    I am in the same situation. I think the ideas about flashing the joists are fantabulous. But how do we accomplish this when your deck boards are in place? Very difficult to work from below. Did you have any ideas or recommendations?

  5. April 10th, 2010 at 23:59 | #5

    It is impossible to do the flashing with the top deck boards in place.
    I used screws to put down my top deck boards, just in case I need to remove the boards.
    MAKE SURE YOU USE SOLAR SEAL BRAND caulk for sealing the flashing to the joists. That stuff is the best! Ask anyone who has used it.

    If your boards are already NAILED down… You’ll have to un-nail them, do the flashing, and then screw them back down. Otherwise you’ll have to create a roof that is hung below the joists. There are some products on the market for this, but they aren’t very cheap.

  6. April 26th, 2010 at 10:44 | #6

    I am also about to build a deck and office below. I was wondering if you thought about using a wooden platform floor or if laying concrete first is the way to go. I thought wood flooring would be less expensive. Thanks.

  7. April 27th, 2010 at 20:56 | #7

    I suppose a wood floor should work. I just wanted a concrete floor. In either case (if your further north like me) then you need to allow for frozen ground heave. Sure would love to see photos when your done.

  8. Jeff
    May 19th, 2010 at 14:41 | #8

    Wow! That looks great! We’re thinking of doing the same sort of thing. Wondering if you installed a gutter (or any other way of diverting the water run off from the trough)?

  9. Bill
    June 27th, 2010 at 09:46 | #9

    Your project sure shows well. Wondering about how your flashing is secured between the deck. Did you nail it in place or is it held by caulking only?

  10. June 27th, 2010 at 14:42 | #10

    I used my air staple gun to fix the position of the aluminum … then the NPC Solar Seal industrial caulk.

  11. Eric
    July 24th, 2010 at 17:27 | #11

    Thank for the information and including a google sketchup model. A question though. How did you cover the wall closest to the house?

    Thanks again.

  12. July 24th, 2010 at 22:56 | #12

    Good question.
    As you can see by the photos… I built the wall tight to the vinyl siding of the house.
    Since that shed wall can’t get any rain or exposure… I didn’t put anything on the plywood.
    The shed’s vinyl corners also help hide the backwall. Even if your standing there and try to see the shed back wall… you can’t, because of the vinyl corners. There is probably a 1 to 2 inch gap between the house wall and shed wall.

  13. Vern W
    August 1st, 2010 at 17:33 | #13

    I wish I had seen this page before I worked on my shed. I have been having a ridiculous amount of issues with water leakage. I had a lot of head room, so when I built the roof I built it lower than the deck, used some 2×4 cross braces to lower it. With that said the roof initially didn’t leak….until winter hit. :(

    Either way I am going to lift my deck boards and add the curved aluminum.

    Just wanted to say thank you Alan for posting what you did, as it will be how I address my shed in the next house. :-)

  14. August 1st, 2010 at 23:26 | #14

    @Vern W
    The biggest secret is using NPC Solar Seal Caulk to seal everything. That stuff is the best caulk I have ever seen. It remains pliable forever. It is used to seal sun rooms which take a great change in weather and temperatures.

  15. Vern W
    August 2nd, 2010 at 17:36 | #15

    Thanks good to know!

    I know you said you used your air stapler gun, but for those of us without any alternative recommendations? I wast thinking screws, but that may require a TON of screws.

  16. Vern W
    August 2nd, 2010 at 21:14 | #16

    Sorry forgot to ask, what size staples did you use? I may end up renting an air stapler. :-D

  17. August 2nd, 2010 at 22:39 | #17

    @Vern W
    Probably 1/2-3/4 inch… The wood trough carries the load … I just needed to tack the aluminum so it wouldn’t move and I could caulk it. The under deck aluminum sheets would be easier if you can give up some headroom. The way I did it does require a lot of patience and a lot of caulk. :)

  18. David
    August 9th, 2010 at 12:46 | #18

    Do you remember what the cost was roughly for materials ?

  19. August 10th, 2010 at 19:43 | #19

    Sorry, I don’t really. I would estimate $1600.

  20. Mike B
    August 12th, 2010 at 19:49 | #20

    Hi Alan,
    First off, great job! Some nice craftsmanship there.

    My question is pretty simple, its regarding the troughs that collect the water. Do they lead to a eavestrough which funnels the water away? Trying to tell from the pics, but I’m not sure if they either hold the water, or if the water flows out below the deck and above the window? Thinking of doing the same at my cottage up north, but the deck is at the top of a steep decline, and i don’t want excess water to weaken the hill at all.


  21. August 12th, 2010 at 22:25 | #21

    I didn’t put in a rain gutter at the end of the troughs, but I could have if I wanted to. In my case the water just flows out each trough and down to the ground. Maybe I will in the future… then again maybe I won’t. The erosion after many years appears almost un-noticeable. However, the extra water at the far shed wall may help explain the extra permafrost lift of the concrete each winter.

  22. Paul J
    August 26th, 2010 at 11:18 | #22

    Wow, nice. This is just what I’m looking for.

    Question, though. Do have any issues with clogging? My deck is, unfortunately, resting under a giant oak, and I have constant twigs and acorns everywhere. I have a couple sheets of plywood under the deck, protecting my hot tub area, but leaves and crap still blow in from the sides… which, of course, cling to bare, wet feet and gets dragged into the house. I plan on making the area a screened-in porch, but I’m worried about the non-removability or your system. It may be possible to flush everything out with enough water, but I figured I’d get your take on it.

    Great job, btw. I LOVE the flashing… it’s so clean and simple.

  23. August 27th, 2010 at 02:22 | #23

    Thanks! I don’t have any trees over my deck or anything that could accumulate in the troughs, but I’m sure that it would rinse away easily with an occasional garden hose flushing down each trough. On a side note… I did just powerwash my deck so that I could restain it and all the crap rinse down the troughs and the NPC solar seal caulk held up to the 3200 psi power washer and my shed roof is still leak proof after all these years!

  24. Tom S Columbus WI
    October 8th, 2010 at 23:38 | #24

    Alan – I just started my project this week – following your concept for the roof/ceiling. Gotta say, it is one heck of an innovative approach and so far – all is going well!!. Questions – how did you seal to the front (near the house where the deck meets the house)? Did you have geometric issues due to the slope [with the aluminum]? My deck is 12×12 with 16″ centers 14-1/2″between joists and I used 1/2″ osb with a 1-1/2″ from top of 10″ joist start with the slope 1.25″ from the bottom of joist at the discharge end. When running from the high end to the lower end – did you have to trim the aluminum much? I have 20″ wide aluminum – putting in tomorrow 10/8/10. I expect I’ll have to trim quite a bit – especially at the beginning of the slope where it’s only 1-1/2″ under the top of joist verses 1-1/4″ over the length of 139″ on the 2×10. Thank you – you should patent this concept (or market it!!! :.)

  25. October 9th, 2010 at 00:29 | #25

    I was surprised that I hadn’t taken a better photo of this. But, if you look in the lower right corner of this pic.. you can make out how I manually cut a piece of aluminum sheet to fit the curve of the trough and create a 45 degree slope into the trough. Then I used my favorite NPC caulk to seal it and hold in position.

  26. Dan
    December 30th, 2010 at 23:00 | #26

    Awesome and exactly what i need to do this spring. What did you use as the flashing on the bottom? How did you start the vinyl, as i see it must not have been level..thanks!

  27. December 30th, 2010 at 23:23 | #27

    The flashing was just a roll of aluminum flashing.
    Yeah, it was impractical to pour the concrete level, so the pad has a slope which I had to account for in building my walls and doors. The siding wasn’t difficult… just cut to match the slope at the bottom and fit into the j-channel, then attach level siding pieces on up.

  28. Jim
    December 31st, 2010 at 14:37 | #28

    Alan – this looks great.

    Curiosity question: if you would have had a little more headroom under the deck, would you have considered installing a flat, slightly angled material, such as fiberglass, beneath the joists instead of the angled troughs?

    I’m planning something similar and debating between troughs between the joists vs some sort of flat panel below the joists.

    Thanks for sharing your design,

  29. December 31st, 2010 at 16:12 | #29

    If I had more headroom then I would have done that, but since I didn’t I’m glad I did it this way. Because when I’m inside the shed, I don’t have to worry about hitting my head. The trough design definitely takes a great deal more time to implement, but it looks and works great when it’s done.

  30. Jim
    December 31st, 2010 at 17:52 | #30

    @Alan Lilly
    Thanks Alan. I’m about your height and would have a couple more inches of clearance under the deck at our new home (but not much more). Taking up all the deck boards doesn’t sound very appealing, so I’ll start sifting through the various options to put something underneath.

    I’d much rather go with your solution … it looks great.

  31. Tim
    March 21st, 2011 at 15:04 | #31

    Love the results. One question: when standing inside the shed there is no “ceiling” correct? Just the exposed flashing between the floor joists?

  32. Todd
    April 27th, 2011 at 20:47 | #32

    Great Shed, it is the exact design that i have to do. My question for you is how did you close the gap between the top of your walls and the deck so you didnt get any snow or rain in there?

  33. April 27th, 2011 at 21:18 | #33

    Great question. As you can see the gap is covered by the overlapping 2×6 skirt boards. The gap is also filled with strips of seat cushion foam… the green foam you can find in bulk at Joann fabric stores. This allows the shed to rise and fall in the winter without lifting the deck. Surprisingly, the shed is well sealed. Not a drop of moisture ever gets inside. I will probably shoot a video of my shed in the spring.

  34. Mike P
    May 11th, 2011 at 10:56 | #34

    Awesome Shed, I’m going to start on my next week and follow your example as much as possible. In your last post about allowing the shed to rise and fall in the winter (I too live up north in South East MN) without lifting the shed, did you mean the deck? I have to use a wood floor, but am really concerned about the heaving. Any ideas on how to prepare the ground before I make the wood platform floor? Sand? Gravel? Both?
    You really have talent and should have (or should) sell this to a “How-To” book, but not yet:)
    Thanks for sharing and all your help!

  35. May 11th, 2011 at 11:11 | #35

    @Mike P
    Thanks Mike. Yeah, I meant “without lifting the deck”. There are a lot of good books on building a regular shed with wood floor… I will check my shed books when I get home for you. You should be concerned about the permafrost layer heaving. Solid ice can lift 10-20 tons per square inch. An elephant weighs 8 tons. Even though the moisture is mixed with soil… it will still have no problem lifting your shed and deck or crushing it until something gives.

  36. Todd
    May 31st, 2011 at 17:33 | #36

    Alan, sorry for all the questions here, but im wondering if you could tell me how did your door for you shed, i dont think ill have enough head room for an overhead or walkthrough door and i like how you did yours?

    Thanks for all your help

  37. May 31st, 2011 at 17:48 | #37


    You can download the sketchup model above to see the exact dimensions of my door. I dimensioned the cedar boards in my woodshop, assembled, and coated with 4-5 coats of epifanes varnish. The tricky part was the fact that my concrete pad sloped downhill, so I had to shape the bottom of both doors to match the ground contour.

    My doors are hobbit doors and I have to duck my head like Gandalf, but once I’m inside the shed I can stand up without hitting my head.

  38. Candace
    June 5th, 2011 at 22:25 | #38

    Thank you so so much! We are getting ready to close on a house and have a different issue with storage. The house we are buying has a deep sloped yard in the back. We are thinking of building a “pier” deck over the slope and I wanted to maximize the space underneath for storage.

    Your shed is inspiring!

  39. Slagood
    June 9th, 2011 at 15:38 | #39

    While I do respect the nice job you did on this…

    Maybe you should have considered moving to a warmer climate where you can sleep outside when the wife kicks you out?

  40. Jane Klembarsky
    July 7th, 2011 at 10:29 | #40

    Thanks for already doing what we were trying to create! We, too, live in very clay-packed soil west of Mpls, MN. My husband and I were wondering – since your shed can rise and fall with the winter frost heave, how did you manage to build your DECK so that IT doesn’t twist and heave? Our neighbors’ decks (built on the north sides of their homes) all heave up in the winter and they have 5′ deep posts on top of foam and they have issues…our deck will be built on the south side of our home, if that matters. Those with decks on the south side don’t seem to have as severe an issue with heaving. We were thinking of just putting the deck right on top of the shed but not attaching it to the house. OR, we were weighing using the Oz Deck post system. Your thoughts on all these issues? THANK YOU so very much!

  41. July 7th, 2011 at 11:07 | #41

    @Jane Klembarsky
    My deck has 2 massive posts (4 glued 2x6s) that are nearly 6 feet deep… that is way below the frost layer. I put concrete at the bottom of my post holes with a couple roof shingles on top of the concrete. Then when I set my posts, as I added dirt, I packed the dirt really hard. By the time the post was set in the hole and the dirt was packed, it felt very very solid and immovable. My posts have never moved since. Since the concrete shed pad was poured around the posts (with relief shims), I can clearly see and measure the amount my concrete heaves in the winter and subsides in the summer, relative to my posts. It is very important that an attached deck NOT heave every winter. Because your deck will weaken and FALL off your house unexpectedly. An un-attached deck should work, but you need to leave a couple inch drop from your door so that the deck surface will not rise above your door threshold in the winter. Otherwise, melting snow and ice will want to come inside.

  42. George Chancellor
    July 15th, 2011 at 19:51 | #42

    I stumbled across your webpage. Love the deck. I have been planning a similar design since we built the house. I too live in colder area (MN), I did my deck in 06, and the patio (shed floor) in 08. My question is did you attach the (or brace) the shed walls to the deck at all? I was looking at placing 1/2″ bolts coming down from the deck to keep the walls from moving since they do not have a roof for support. My thought is that if I do not support the walls with the deck then a nice wind storm may damage the walls. We get a nice wind tunnel effect in the back yard, since it is all open (new subdivision)
    Yes when I attach the walls to the deck there will be 3/4 -1″ space between the wall and deck for heaving. How did you handle this and have you had any problems with the walls swaying? Also my deck is 22 x 16.

  43. July 15th, 2011 at 21:29 | #43

    @George Chancellor
    My walls are completely unattached to the deck. I did bolt the walls to the concrete slab. I built the shed with 4 walls, not just 3 and put strong 3/4 plywood sheathing on the outside. The walls feel very very strong and stable without sway or movement. We’ve had 70 mph winds and the shed is rock solid. In the last picture you can see I wrapped the deck floor with a skirt board which hides the gap very effectively and completely prevents driving rain, snow and wind from causing trouble. I cut oversized strips of quality seat foam (from Joann craft store) and filled the gap between the shed walls and the deck. Anyone that looks a the shed (inside or out) doesnt even notice the gap. The shed appears completely solid and sealed. When I get time I plan on shooting some detailed video, inside and outside so that everyone can clearly see its construction. Good Luck! Be sure to send pictures of your deck shed!

  44. jeffrey
    May 15th, 2012 at 21:31 | #44

    how much did the shed cost you to build????

  45. May 15th, 2012 at 22:01 | #45

    I can’t honestly say. It’s been a while since I built it. If I were to take a guess … I’d say, I spent more to build the small deck above it and that was about $1700. Having the concrete pad poured for the shed was the most expensive. There isn’t much to the shed as you can see… just some 2×4′s, plywood, a cheap window, vincyl siding (second most expensive), some cedar for the doors and a bunch of nails, screws and misc.

  46. Adam
    May 29th, 2012 at 13:48 | #46

    Hi there, is there a need for the back wall to actually be built? or could you just cut off the siding from the wall that the shed will face and attach this thing right to the house utilizing the house wall as the back wall?

  47. May 29th, 2012 at 19:33 | #47

    Probably could have done it that way … I didn’t want to dismantle my house siding. Having a 4th wall didn’t cost that much in time or materials and seemed more practical for me. I didn’t put any siding on the outside of the 4th wall facing the home.

  48. Adam
    May 30th, 2012 at 20:07 | #48

    just got a quote to get this done – 15,000CND! This includes taking old deck off ..

  49. Paul
    September 12th, 2012 at 21:32 | #49

    I have a theory on how you could install the aluminum under the deck without taking the deck boards off.
    Cut strips of aluminum about 3 or 4 inches wide and the length of the deck. Install them to the sides of the joists sloping down away from the house.
    Use the calking and fastening method of the gentleman above, but make sure that the calking and fastening is done on about the top 1 to 1-1/2 inches. After fastening the strips, bend the bottom of them away from the joists just a little. Then bend the wide piece of aluminum to the shape that this gentleman has done. Push this wide piece of aluminum up between the long strips of aluminum and the joists on both sides. Hold the wide piece of aluminum up with the same wooden system that this gentleman used.
    If you are really worried about rotting joists, you could install the long strips of aluminum all the way up to the underside of the deck boards and cut them so that the the bottom side of this strip slopes down away from the house.

  50. carter newton
    October 6th, 2012 at 13:24 | #50

    Impressive and well done and narrated. We will try the same thing. Help comment was the heaving of the concrete which I would not have understood.Thanks

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