Raised flower bed beside house?

gcomer123

Hi all - our back garden is just all concrete. At some stage we'll probably have to take some of it up or deck it or something, but for now we're trying to find a cheap enough way to make it a bit more like a garden! What we're thinking is of making a raised flower bed that runs along the back of the house.

Idea is we corden off a section (prob 7ft long by about 4 ft deep) and make a flower bed. We were thinking of putting wood around the back and side (ie the bit that runs along the house, and along the dividing wall with next door). Then at the front / side you can see make a little wall with stone / granite or something. The whole lot will only be 15-18" deep, and then we just put a plastic sheet down and fill with soil and start planting.

What we're worried about is the drainage / damp aspect of having this (what is in essence now a giant flower pot) that near the house. The garden slopes a bit from the house down (about a 6" drop from house to end of this flower bed). So the water should run out of the bed away from the house if we leave some holes in the plastic sheet and some drainage.

However we're worried about running the bed right up to the house wall. We were thinking of leaving an inch or two gap between the house and the start of the bed, but are worried if we do this will we end up with a rain trap where teh water falls into this gap and has no where to go? We looked at putting in a waterproof membrane, and maybe this is the way to go.

Again - we're looking for something which is cheap and cheerful and were hoping to have the whole bed made and ready to go for about €200 or so.

If you were us what would you suggest to make sure we dont end up with damp in the house from this?

Cheers

Orion

Damp shouldn't be a problem. The soil will retain the moisture. I recently made a raised bed and use old scaffold planks from a builders providers for €3 each which would probably be ideal. You shouldn't need the plastic sheet if it's concrete - the sheet is more to stop weeds coming through from underlying soil than to damp-proof it. A sheet of waterproofing between the soil and the wood is recommended by some people but I didn't bother - retired scaffold planks are well seasoned anyway.

gwjones42

I recently made a raised bed out of decking planks so it looks good on the outside. I was worried that the weight of the soil inside would cause it to bulge and fall apart, so I built it with two walls. The inside wall is just plywood, but it's marine standard so should be water resistant for a few years at least. I left space of about two inches between this wall and the decking planks on the outside and filled it with cheap gravelly stones.

Building something similar would be a way for you to avoid having damp soil against the wall of your house.

Minder

I would avoid bridging the damp proof course in the brickwork of the house - a scaffold board pressed flush to the brickwork will act as a moisture bridge and may cause a damp problem inside.

If the concrete slab is not too thick, drill some drainage holes near the house to avoid a rain trap.

gcomer123

Hi all - thanks for the advice so far. So what I'm hearing is:

1 - I don't need the plastic sheet and it might in fact help the drainage away from the house if I dont have one. The area I'm using has about a 6" slope away from the house as is.

2 - 2nd wall - it might make sense to make a 2nd wall with chipboard or something to help strengthen as well as keep the outer wall dry. OR else I could simply leave a gap between this and the house of a few inches and make sure there is drainage in that gap away from the house.

thanks for the advice and keep it coming!!

Sonnenblumen

gcomer123 wrote: »

Hi all - thanks for the advice so far. So what I'm hearing is:

1 - I don't need the plastic sheet and it might in fact help the drainage away from the house if I dont have one. The area I'm using has about a 6" slope away from the house as is.

2 - 2nd wall - it might make sense to make a 2nd wall with chipboard or something to help strengthen as well as keep the outer wall dry. OR else I could simply leave a gap between this and the house of a few inches and make sure there is drainage in that gap away from the house.

thanks for the advice and keep it coming!!

When you build a Raised Bed above the DPC line of the house you need to be very careful not to bridge/undermine the DPC. An RB with a dry planting scheme may not be a major risk, but RBs are generally moist areas and the wall should be protected.

Plastic membrane is one method but also a timber barrier can be good. Obviously the choice of timber needs to take account of the growing moist environment. Marine ply might be good but chipboard would be useless, and rot in no time. Using Pressure treated timber is the preferred way, deck boards are IMO too thin and we would prefer to build a more substantive line using PT timber against the wall, eg PT Pine Sleepers which are 100mm/4" thick. Also exterior walls are rarely 100% flush so any discrepancies between timber line and wall finish provides minute but useful air circulation and prevent any mositure spots.

People tend to be fearful of RBs at or near walls, but if constructed well with proper materials there should be no problem. Also timber choice must consider also the preferred planting. For example, Bamboo plants will require a much more robust construction than say an RB of Ornamental/Herbaceous plants.

No need to put liner on base over concrete, if anything, you could place some rough stone which will alleviate any risk of water build up at bottom. A useful labour saving tip involves lining the base with a heavy duty PVC to create a water well. This will capture some water and with a few strategically placed heavy duty cotton wicks to absorb water from base, can be interwoven in soil around plant rootballs to provide a useful means of irrigating the plants via cappilliary action.

Good luck.

gcomer123

i think the plan is to leave a few inches gap between the bed and the house to stop the damp from the bed touching off the house.

So between the house and the soil will be plastic, some treated wood and an inch or two gap. in this case we should be fine yeah?

granite man

gcomer123 wrote: »

i think the plan is to leave a few inches gap between the bed and the house to stop the damp from the bed touching off the house.

So between the house and the soil will be plastic, some treated wood and an inch or two gap. in this case we should be fine yeah?

Make sure you use a good thick plastic with no holes in it. Skimping on this could cost you very dear in repairs.
Building regs recommend that hard surfaces should finish 150mm (6") below the dpc level which you will find to be level to your front door base. Even wood bridging that will enable moisture to filter through, make sure the plastic is touching the wall before anything else does and be careful when watering to make sure it doesn't get through either. Best of luck.