low level deck

[shane37]

I’m looking at building a deck over a concrete patio and extending it out over the grass. It’s only in the planning stage atm. The deck will be 7400x3800 and the concrete patio is 5000x2500. Looking at having it sit flush with the brick sill with the sliding doors. The sill is only 75mm above the concrete and looking at using 90x45 joists and 137x23 ecko decking. What is the best option for joist supports on the concrete patio with such a low clearance? 

[MitchellMc]

Welcome to the Workshop community @shane37. I'd be happy to kick-off the discussion.

If we take the 75mm and minus the Eko Deck thickness we are left with 52mm for our bearers/joists and supports. That's not a lot of room, an option might be Dynabolting through the timber straight into the concrete with Ramset 6 x 100mm Dynabolt Plus Flat Head Bolt 2 Pack. You would need a 7mm spacer under the 45mm timber to bring the finishing height to 75mm and flush with the sill.

I'm a little concerned about air-flow/dampness in such a confined space and would be interested to hear from some of our knowledgable members their thoughts. Let me mention @ProjectPete, @Brad, @Adam_W to see if they may like to offer some helpful advice on the situation.

I look forward to hearing what our helpful members would do in this situation and following along with your build.

Mitchell

[shane37]

Thanks @MitchellMc , will using h4 timber help this issue? 

[MitchellMc]

Hi @shane37,

Using H4 would certainly help with the issue. The H4 combined with the Eko Deck would ensure nothing would be adversely affected by potential moisture build-up.

Mitchell 

[Brad]

If it is the original style Ekodeck I would open the gap between boards to 8mm to aid airflow ( I will miss the old 88mm decking ) which if it is the new style I think the gap is set by the clips.

I normally like the Goodtimes Adjustable Feet but 7mm may be too tight for the foot but you may be able to counterbore to give a bit more room for adjustment.

I would use a spacer between the joist and the brick if the joist was running parallel so that there is less chance of moisture being a problem.

[shane37]

Thanks @Brad ,it is the new ekodeck plus which has 5mm spacing between boards. I’m contemplating using h4 timber for the joists and bearers as @MitchellMc  said this may help with moisture buildup from the lack of clearance but I’ve read that sometimes h4 might not be straight. Would this be an issue with the sub frame? 

[Brad]

Not only H4 that can have issues with straightness, my choice with any timber is picking through the pile to get the straightest ones/best appearance depending on the job and not relying on random selections to be picked up or delivered. If you buy a pack to get a cheaper price you will get some that needs to be worked around. H4 would be my choice and with some skill you can fix most straightness issues by either planning your cuts or careful clamping.