Low clearance decking over patio

[Nuclear Fusion]

I'm looking to deck over an existing patio, the main issue is the low clearance from the door sill. There is roughly 75mm from the patio tiles to underneath the door sill and 100mm to the top of the door sill. Therefore I would need to use thinner joists or lay them flat.

Will it be a problem to use 2x4 timbers layed flat along the patio? I figured it will be supported in more places so it would hold up. What is the best way to keep the timbers off the patio itself (in terms of dampness)- plastic packers/shims? Additionally, the patio has lots of gaps between the tiles where the cement has crumbled away and weeds grow through, I was planning to repoint these to prevent the weeds. Do I need a weed proof membrane under the joists as well?

Thanks

 

[chalkywhite]

Weed proof membrane would be belt and braces yes, but lack of light through deck would keep most weeds at bay.

I've used thin strips of roofing felt under joists before to keep the beams from getting damp.

Personally, I wouldn't go back to a deck again, much prefer slabs

 

[Nuclear Fusion]

Yes I'm thinking that I might actually replace the patio instead, factoring in longevity. Thanks!

 

[chalkywhite]

The previous owners of our house repaved over the top of existing concrete "council" slabs with a York stone look paver. Looks great, just be careful not to go higher than your DPC