How to build a low-level deck with only 50mm clearance?

[kalindug]

Hi all, 

I am planning to a build a deck for my alfresco area. I have a very low clearance 50mm. 

Can we still built a deck on this slab?

Also, I have 75mm ish clearance from window rail to slab. Can we utilise that space or the deck has to be built under the window rail?

I really need this deck (I promised my wife 😶)Would be great to hear from any of you. 

Thanks.

[MitchellMc · Accepted solution]

Welcome to the Bunnings Workshop community @kalindug. It's terrific you joined us, and many thanks for your question about deck construction.

Even the 75mm would be an exceptionally low height for building your deck within. You could have the deck flush with the door frame, but you need to have it set back away from the house wall to stop water egress. If you want to bring it close to the door frame, you'll need to do some work with flashing to ensure water doesn't penetrate the wall. Any lip at the doorsill or step down onto the deck should be easily distinguished as not to cause a trip hazard.

You'd need to employ some slightly unconventional techniques to build a deck within 75mm. 19mm will be used for the decking timber, which leaves you with 56mm for the frame and clearance under it. You could use 90 x 35mm H3 MGP 10 Treated Pine Outdoor Timber Framing on its face, which will leave 21mm clearance for drainage and airflow. 21mm is not much room, and you should expect to see the deck's life reduced due to it.

If you haven't already, make sure to have a read of @Adam_W's guide on How to build a low-level deck.

Please let me know if you have any questions.

Mitchell

[Adam_W]

Hey @kalindug , @MitchellMc has hit all the right points there.
Basically in this situation you are really putting battens on the slab to lay the deck on. The trick will be making sure you can maintain some airflow beneath and avoid water running back to the house.
You could extend the deck out past the slab end but you'd need to switch to a more conventional method and leave an 'outrigger' length on your battens protruding so you could join to them if you get my drift.

[Chrisb1]

Hi Mitchell

Just a question on your suggestion re using the 90X45 on its face.  

I'm in a similar position as the original poster but have a little more room to play with.  Excluding the deck board, I have around 90mm at its lowest.  I originally wanted to use 90X45 but due to the clearance was going to change to 70X45 and double them up (doing the 70mm vertically).  Do you think it would be better to do that or use 90X45 on its face?  I thought with the natural flex, if I was to use 90X45 on its face, I'd need to use a lot more footings (stirrups in my case) to keep it level and reduce movement?

Can you let me know which way you think is better

Thanks

Chris

[MitchellMc]

Welcome to the Bunnings Workshop community @Chrisb1. It's great to have you join us, and many thanks for your question about joist orientation.

I'd recommend the two 70mm timbers laminated together with glue and/or screws. Two 70 x 45mm timbers joined together vertically would exceed the spanning capabilities of 90 x 45mm timber on its face. Even if the 90 x 45mm was vertical, the two 70 x 45mm timbers properly laminated together would likely exceed its capacity. If you have the room, it's always best to have the timber on its edge instead of on its face. Since the two 70 x 45's can span a greater distance, you'll require fewer footings and supports.

Please let me know if you have any questions.

Mitchell

[Chrisb1]

Thanks Mitchell

Makes sense so will go with that

Cheers

Chris

[kalindug]

Thanks Mitchell for you expert ideas. 

We will go with 90 x 35mm and hopefully wouldn't much issues with clearance.

Thanks again. 

[MitchellMc]

Keep us updated, @kalindug and reach out if you get stuck. We're here to help.

Mitchell

[kalindug]

Thanks @Adam_W . 

I showed this to my landscaper and he said he'll get it done. 

Hopefully it'll look good once complete.