How to build a deck over concrete step and flush with door sill?

[asw]

Hi, currently building a freestanding decking with our decking boards running parallel with our home. We have a concrete step and a brick nib which we want to the boards to run over. What is the best way to do this? We also want it to be flush with our door frame but don't want to cover the weap holes. What's the best way to go about this? 

 

 

 

[JacobZ]

Hi @asw,

Welcome to the Bunnings Workshop community, it is wonderful to have you with us.

Unfortunately, I don't think there is a good way that you could run your decking boards over the brick sill and concrete step because there needs to be clearance beneath the boards to allow for ventilation and for water to drain.

If you were to run your boards over them, especially with them being parallel to the house, water would be trapped between the boards, where it would sit and cause rot prematurely.

You would be much better off having the decking boards finish flush with the top of the brick sill and step. That way, there would be gaps around the decking boards that would allow water to drain through.

Covering up that vent is also a bit problematic, as it needs free-flowing air for it to be effective. As you want your boards to run parallel to the house, the framing would be perpendicular to the house, so if your joists are spaced so they don't impede the vent, this would maximise the airflow to them, although it is still not a great idea to cover them in any way.

Allow me to tag or knowledgeable members @Nailbag, @AlanM52 and @JoeAzza for their thoughts.

Jacob

[asw]

Hi JacobZ thank you for your advice! If we were to have the decking boards flush with the brick sill and step, is there any suggestions how to make it look a little bit more seamless? I think it would look a little strange with the concrete step and brick exposed amongst the decking boards

[JacobZ]

Hi @asw,

If you cut them so that the gap around them is consistent, then it would still look nice. I have seen decks built like this before and trust me, they still look good.

The problem with adding anything over these seams is that you are creating a spot for water to get trapped, which is the single most detrimental thing that can happen to decks like this.

You have to weigh up aesthetics with the overall longevity of your deck, because any pooling water is going to drastically reduce the lifetime of your deck.

Let me know if you have further questions.

Jacob

[asw]

Thanks Jacob. Would this still be an issue if the decking was uundera pergola? We don't get any water coming through. Would you happen to have any examples of what you suggested or some sort of diagram? 

[JacobZ]

Hi @asw,

You'd certainly be less at risk, but with heavy winds or heavy rains, you can still get water blowing in under a pergola. 

Ultimately, this is your deck and you can do what you wish, but I think it's important to be aware that water can and will reduce the life of your deck if it gets in.

Basically, as long as the gap between the decking boards and the sill and step is consistent, for example, let's say 5mm, then the transition between the two will look relatively seamless.

Check out @maknilsin's Backyard makeover with new deck and planter boxes, where the decking boards finish flush against the brick sill of their home. It's not exactly the same scenario, but it is the closest example I can find.

Let me know what you think.

Jacob

[Nailbag]

Hi @asw 

the first thing that came to mind was along the same recommendation as with @JacobZ in that you should definitely run the boards into the house and not parallel. 

The first reason is that it will allow for any issues with the all of the house running out of square. The joists will be easier to work with running parallel to the house thus allowing the ends of the boards to be cut precisely where they meet the wall and most importantly flush to the sliding door frame.

You also have ample height from the looks to use 90mm x 45mm joists sitting on top of adjustable mini-feet. With the gaps in the deck boards and clearance in the subfloor I think you should still have ample ventilation for your brick ventilation. Just avoid blocking them with the joist of one of the feet.

Nailbag