How to build decking between two walls?

[gspencer]

Hi, I am planning on building a deck that is 2.5m x 5.5m and runs between the house and a besser block wall. It non-trivial to install stumps in the area so I was hoping to attach the bearers directly to the two walls and then run the joist between them.

Firstly, will that work, and if I am using 140x45 bearers do I need to jsut ensure that it its supported by the wall according to the span table (i.e. every 1.4m)?

Secondly, what is the best way to affix the bearer to the walls, one side is solid clay brick or solid concrete, while the other side may be hollow besser bricks (may be concrete filled..).  I was thinking  16mmx140mm Dynabolts directly into the brick, but didn't know if that would work into besser blocks. Any advice?

[JacobZ]

Hi @gspencer,

Thank you for your question about building a deck between two walls at your property.

When a deck is a standalone structure, it is relatively simple to install some stumps following the span tables to ensure it is going to be solid. When you introduce lateral attachment to existing structures, their structural integrity and suitability for the job need to be taken into consideration. 

While the materials selected are a suitable calibre for the job, I would not be confident building a deck that is exclusively supported through lateral attachment to existing structures without having a structural engineer give it the all clear.

If it is deemed ok by a structural engineer, they would need to recommend a suitable method to affix the bearer to the walls.

If you built the deck as a standalone structure, I would have much more of an ability to assist, but unfortunately, I am not qualified to assess an existing structure's suitability for a job like this.

Let me know what you think.

Jacob

[gspencer]

Thanks Jacob,

I think I will have to rethink my support plan. On a different question, I am building this on the south side of the house which is pretty much constantly in shade. I was planning on using Merbau decking but was wonding if that was the correct choice? 

[JacobZ]

Hi @gspencer,

Being in the shade doesn't limit you. If anything, being in the shade is beneficial as the decking won't be exposed to harsh UV rays, which can speed up the deterioration of materials.

Merbau would be an excellent choice for your deck, but there are certainly other options for Timber Decking such as Spotted Gum, Jarrah and Blackbutt. Due to differences in regional availability, it would be best to contact your local store to see which options are either in stock or can be ordered.

There is also EkoDeck, which is a composite decking product that comes in a variety of colours and requires zero upkeep besides a good clean every now and then.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob

[gspencer]

Hi, if I was to bring the stumps in from the walls to allow for the hole, how far past the bearers can I have the joists run?

[JacobZ]

Hi @gspencer,

Your maximum overhang should not exceed 30% of the backspan. As an example, if behind the overhang, your joist spans 1000mm between the bearers, they can overhang the bearer by 300mm.

300mm is usually the most I would advise without speaking with a professional, but that would certainly give you a good amount of room for your stumps.

Let me know what you think and if you have further questions, please don't hesitate to ask.

Jacob