Decking query

Catslovelycats

I’ve just had decking installed but the men put the joists down before the membrane. The membrane is fitted between the joists and the decking boards. They say that’s because it’s more efficient at stopping the weeds growing underneath. Is this right? I’m concerned that if the joists are on ground they are more likely to be damaged by wet?
Thanks

Grenage

Are the decking cross-members not raised off the floor and attached to posts? That's how all the decking I've pulled apart has been constructed.

The membranes don't stop water, just weeds, but I would have thought having it directly under the boards would just trap damp debris around the boards - which would not be desirable.

If the cross-members are directly on soil, then yes they will rot eventually; possibly not until after the boards, but they should be off the soil in some manner.

Aylesbury_Duck

Sounds dodgy to me. Firstly the joists should be raised off the ground. Secondly, that makes it easy to fit one span of weed-suppressing membrane.

Your joists will eventually rot faster through being in contact with the ground and the membrane being in sections just creates more gaps for weeds to grow.

Davesnave

They're possibly having you on, but if the details of construction weren't agreed before they started, you have no grounds to ask for it to be changed now.

Properly treated bearers will last a reasonable time, but we don't know if they were or weren't or what sort of site preparation there was.

It's a learning curve. Even if you don't plan to do the work yourself, you should do research and find out how it should be done. There are various ways, but bearers placed onthe soil surface, with or without polypropylene under them, isn't the best. Concreting-in uprights to carry them is better, but again, we don't know if you paid appropriately for 'better.'

PasturesNew

The membranes, existing or not, fully covering or not, won't make an ounce of difference to whether the joists rot or not. They'd still be exposed to exactly the same levels of damp/water etc.

Catslovelycats

Grenage wrote: »

Are the decking cross-members not raised off the floor and attached to posts? That's how all the decking I've pulled apart has been constructed.
.

I didn't see that part of the construction. It could be my fault - I just assumed everything was on the same level but it may be raised off the floor.
They're coming back today to replace a fence that they damaged (at my request, it must be said!) so I'll ask them. Thanks

Catslovelycats

Davesnave wrote: »

They're possibly having you on, but if the details of construction weren't agreed before they started, you have no grounds to ask for it to be changed now.

Properly treated bearers will last a reasonable time, but we don't know if they were or weren't or what sort of site preparation there was.

It's a learning curve. Even if you don't plan to do the work yourself, you should do research and find out how it should be done. There are various ways, but bearers placed onthe soil surface, with or without polypropylene under them, isn't the best. Concreting-in uprights to carry them is better, but again, we don't know if you paid appropriately for 'better.'

I did a lot of research online and had several people come to quote me. I knew exactly what I was getting and how the job would be done, they just didn't specifiy where the membrane would go and I had always assumed that the mebrane went on the ground. However, some canny googling this morning has revealed that some deckers do attach the mebrane sheet under the planks rather than on the ground. Everything they used is pressure treated. No, I didn't pay for concreting in. Thanks

Catslovelycats

Thanks everyone.