Garden help

[Justanothergeordie]

Hi all – I need some help working out what to do with part of my garden. At the back of my house I've some large sliding glass doors which lead out to flagstones about 7m wide by 4m deep. Past that there's a grass lawn with a path of the same flagstones down one side. The step down to the flagstones is 20cm from the doors. There is a medium size tree at the end of the flagstones and the roots have made the flags all buckled and uneven.

What I originally wanted to do was deck the whole 7m x 4m flag area up to the grass but I'm not sure if 20cm is deep enough to work with having never done anything like this before. What I'm wondering is, do I need to take up all the flagstones to increase the depth and level the area off or just take out a few then dig holes and add some supports?

Any other cost-effective options would be very helpful. I've considered adding gravel on top of the flags up to the height of the back door but didn't want to add any more flagstones as the tree might wreck them over time. Cost is an issue so I'd like to try to do this myself.

Thanks!

 

[r896neo]

Avoid gravel over flags its like marbles. You could deck the area without removing the flags. Normal practise would be 150mm x 50mm joists with 32mm boards which puts you very close to 8''(200mm)

You could use 4x2 joists and just beef up your supports by making them closer together. You would want at least an inch, Ideally a couple of inches, under the decking for ventilation and water flow.

 

[Justanothergeordie]

Thanks for the reply. Do you mean just put a frame on top of the flagstones without adding any posts in the ground?

 

[r896neo]

Yes if your happy the patio isnt going to move significantly you can use them as support. You will need to space it off the ground obviously with perhaps off cuts of paving flags, bricks, tiles or any masonary product.

If your very concerned the patio is really moving significantly then cut holes in it and use posts concreted in.

 

[Justanothergeordie]

Thanks. I'm fairly confident about how to build it, my only concern is the movement bit you just mentioned. If the tree's matured I can't imagine it's going to move the flags too much any more?

 

[hansPulesh]

How far is the tree from the flags where you want the decking to be?

What are the current flags like? Are they in good condition?

 

[Justanothergeordie]

Hi –

The flags have been planted around the tree but not completely all around. The final row of flags have one or two missing where the tree sits. The roots have quite obviously moved the flags around the tree as they're not flat. The rest of the flags are pretty uneven too though not too bad, they're very stable. It's a mature tree and hasn't grown much in the 6 years we've lived here and I don't think the flags have moved in that time either.

I'm wondering if I concrete some posts in, will the decking bow slightly where it's near the tree if there is movement? I was hoping to get away with just sitting the frame on the flags as the decking will end about 30cm before the tree.

Thanks for any help.

 

[hansPulesh]

Ok, to be honest, unless you take that tree out, you're always going to get movement depending on its growth/weather. When you lay the deck frame down, you'd normally construct the frame, sit it in place on top of a few bricks, level it out and then attach the legs to the frame. (I'd also advise that you use a damp proof material under the leg so that any (rain) water slides away from the leg and is not soaked up by it.

You can rest the legs on the flags but if/when they move, the deck frame resting on them will move too. I wouldn't underestimate tree root strength either, they literally can move houses!

If you can see where the roots are, try placing the legs on flags unaffected by the roots?

 

[Justanothergeordie]

I'll try and work it so to avoid having legs near the tree. When you say damp proof, I knew I'd need something but is this a sheet, something you paint on or something you stick on from a roll?

Ta

 

[hansPulesh]

You can buy a roll of something called a damp proof course from most builders merchants/DIY stores.

 

[Justanothergeordie]

Great stuff thanks. I don't suppose if you or anyone else reading has any experience with composite decking? We wanted to stain ours opaque grey rather than traditional wood colour when it's finished but I was checking out the grey composite which apparently doesn't need much aftercare (although it looks a bit pricey!)

 

[hansPulesh]

It is pricey.... especially if you have a large area to cover. Standard wooden decking generally looks after itself but needs washing and cleaning and then oiling at least twice a year. I'd use the Ronseal stuff as the cheaper shop's own brand stuff is useless!

 

[Justanothergeordie]

Noted - thanks a lot

 

[hansPulesh]

No problem

 

[Justanothergeordie]

Have you done many decks before? I'm wondering if I really need to concrete posts in or sit the farm on top of the flags?