Salvage my decking project!

[Andehh]

Hi guys,

I originally signed up to this forum for some pipes knocking and have just stumbled across this particular sub-forum! I wish I had 3 weeks ago when i started my decking though....

Long story short for the last 3 weeks I have been chipping away at a 27m^2 decking in my garden. I was having problems growing grass behind my house due to a total lack of sunlight and clay soil. The soil is very very heavy clay, from about 20-30mm below the surface. From a few inches down it can be thrown at a wall and will stick for weeks (i had to try it! )

I got 4 quotes for decking, all coming in at over £2500 - £4000. After piecing together all of their advice and asking a few guys at work and reading several wickes/b&Q guides to decking I decided to give it a go myself! |total cost is around £1200.

I don't think I am a million miles off the mark but i have read several things I wish I had known before i started...

--I am using 75mm x 75mm posts, not the 100mm x 100mm advised.
--I am postcreting them all in to a depth of around 25cm, 1.5 bags of crete per hole.
--Each post has 4 layers of Ronseal Total wood protection, concrete posts slope away so no puddling water at the base of the post.
--Semi-water proof membrane under everything to prevent raising damp.
--Each joist (1500mm x 50mm) is about 20mm above the mud.
--The deck slopes away from the house.
--The Joists are around 450mm apart, 700mm around a big sewer drain which maybe one day will need access. I plan on creating a 'box/noggins' around this to reduce the distance as much as possible around/near it.
--The posts are every 800mm-900mm along the joists


Now, my questions;


Are Noggins really that essential? i plan on putting in several around the wider-ish areas/areas I think will have most traffic but I wasn't going to do the entire decking.

Is the weed membrane/semi-water proof layer a good thing or a bad thing? I was trying to combat rising damp/wood sitting near damp mud, but I don't want to prevent water not seeping through...

The area where it is dampest I have dug a 2 foot deep trench x 4 feet to act as a 'sink', i was going to fill this with the largest sized pebbles I could buy (1 tonne bag type..). Is this a good idea? It is 2 feet from each of the 4 posts which surround it.

The planks will slope into a ''flower bed'' which is against a supporting wall (neighbours garden above mine). This flower bed slopes towards the decking, I have removed the water proof membrane below this and it will have about 15cm of bark from lip of the deck to mud below. Is this going to be a big problem? I am doing to plant as many boggying loving plants as possible to soak up as much water.

I have attached a picture to give you guys an idea! Whilst I no this deckign wont last as long as it would had I used 600mm deep holes & 100mm posts I hope it will last a few years at least!

http://dl.dropbox.com/u/72120595/IMG_20120416_200029.jpg

 

[r896neo]

Noggins are essential, they will really help the rigidness of the whole structure.

The membrane should not be waterproof, something like landscaping fabric is better.

The sump will have little effect on very heavy clay soil as water will just gather in it not soak away.

The amount of run off on a deck is quite small really so don't worry, running into a flowerbed would be fine.

Dont' worry about your posts 100mm would be better but 3x3 will be fine. As for hole depth its mainly to get into good ground sometimes this is at 300mm sometimes 450, 600mm is overkill in my opinion. All you need is a solid base under the posts.

 

[Andehh]

It is weed membrane I believe, but seems semi water-permeable?

I see on the trench, I will fill it with as much gravel as possible anyway. it was mainly somewhere for surface water to go to as I don't want it puddling around the posts!

I will buy a few more joists to use as noggins in that case, shouldn't see them being too taxing to add!

 

[r896neo]

no won't be too time consuming, just skew nail them in.

 

[Andehh]

Noggins will be used then, I have factored them into my next pit stop at B&Q! I will buy a couple more joists and cut them down i think.

As for the weed membrane, is this likely to do more harm then good covering the soil under the joists? The joists are all lifted off the soil slightly, but are in contact with the membrane.

 

[r896neo]

It obviously should not be in contact with the timber. but in general it will be fine, remember it will be getting less direct water on it once the deck is over the top so more time for water to get through it.

 

[Andehh]

Many thanks mate!

Any other suggestions before I start adding the niggins and hopefully deck boards as soon as the weather clears would be gratefully received!

 

[r896neo]

Personally i prefer smooth side up, its partly just personal choice but it is no less slippy and much easier to oil and keep clean.

With decking (especially as your area looks a little shady) so much of it looks awful after 2 years because its not maintained and anything that will help you maintain it you should do.

If you haven't got screws yet, the spax torx head ones are the best in my opinion. Don't use crap green/brown ones.

http://www.screwfix.com/p/spax-deck...-_-Spax Decking Screws 4.5 x 60mm Pack of 200

 

[Andehh]

Well you were right on the money with my draining trench. It is currently 90% full of water (2 foot deep x 1 foot wide x 3-4 feet long) and that's before I went ahead and added rubble/pebbles!!

This damn drought we are suffering!


I was planning on doing ridges down, but will have a look at several of them laid down to see which side I prefer when I am closer to the stage of screwing them in!

I am using these screws and doing 3 per joist-support. Each one driven in hard. I am just about to buy a second pack of them (of which only approx 25 are required), so will prob go round and put a fourth in just for good measure!
http://www.screwfix.com/p/power-fast-screws-6-0-x-100mm-pack-of-100/40984

I then have some (...1,3000) small 4 x 60mm ones to hold the decking boards in place!

 

[r896neo]

2 per board per joist is plenty. Can you return those screws? they are not really for outdoor use and will rust very quickly making them almost impossible to get out and to lift boards should you need to down the line a bit.

That said many of the so called outdoor screws are little better.

 

[Andehh]

Oh bugger!

I am sure I saw somewhere that they were plated, or at least galvanised. I will reject the second pack of them tomorrow when I was going to pick them up!

In the meantime best I start looking for some replacements. Knowing how difficult it was to remove a couple of them trying to remove the rest (100!) is gunna be a real hateful task!

edit:

Hows these? I do like the extra length, 100mm seems to work perfectly!
http://www.screwfix.com/p/turbogold-xt-screws-6-x-100mm-100pcx/46230

 

[Andehh]

With the soil being modeling clay consistency and draining away a very slow process is the weed matting going to hamper any evaporating/prevent a breeze getting to the soil under the deck?

I am not sure what effect weed matting had on drainage.:

 

[Andehh]

If anyone can comment I'd be grateful!

Thanks

 

[r896neo]

I would still go for the fabric as it will stop weeds coming up through the boards,

The other technique is to staple it to trhe under side of the joists but this is pretty fiddly