Repairing a summerhouse floor

Hello, looking for advice on the following please? The summerhouse we inherited last year when we moved in is in a pretty poor state. The timber around the bottom edges of the base were rotten so I've removed them but the tongue and groove floorboards are also rotten for about an inch all the way around so that they will either have to be repaired or replaced so that the walls have something for them to be fixed to. Please can anyone tell me is it possible to repair, if so how would I go about it or would all of the boards need to be replaced which would be a real pain given that they are nailed to joists under the floor. It's a 6' x 8' octagonal building with a total of 21 boards, I've attached a photo of the floor from the installation instructions. Thank you

 

If I'm seeing this right the sides are supported by the floor.
And the floor under the sides is rotten?

 

Is it like this one?

Oxfordshire Octagonal Summerhouse

If so, maybe the manufacturers could supply and fit a new floor for you?

 

Because it is timber it can be repaired or replaced, even if dismantling is deemed necessary to perform the task.
The most important thing is that it is done with decay removed and substituted with timber that is suitably treated to prevent /protect from future decay. It may be advisable to ensure that the building is stable and that this is suitably supported both now and in the future.
When selecting materials look for pressure treated timber such as this* and take the trouble to further treat both the new and existing sound wood with a 5 star preserver such as this#
*Search exterior timber | Wickes.co.uk
#Barrettine Universal Wood Preserver - Clear - 5L | Wickes.co.uk
It appears that this pattern of summerhouse might cost £2-4000 to replace , giving a considerable potential budget value in saving the existing.

 

Could you post a picture of where the rot is please?

 

Photos of the actual structure inside and outside would be helpful.
What do the joists sit on?
I would be concerned that the sides rest on the edge of the floor, so water can get trapped there. It would be better if the floor was completely inside the sides, so the sides come down over the floor edge and the water can run off onto the ground

 

I had the same problem with my inherited one but had to demolish mine as the manufacturers would not supply me with any replacement timber pieces. When demolished there was no damp proof membrane with no ventilation and it was rotting from the base up. New one looks great.

 

Yes Pete you are correct, the sides are supported by the floor and it is those boards which are rotten around the edges.

 

Morning all, many thanks for your replies which are much appreciated. The building was made by Alton who I believe are no longer trading but I could be wrong there. I have contacted the Greenhouse People who sell a have a very similar building under a different name but the dimensions are not quite the same and they can't help with replacement timber. This is about 20 years old and has been on a concrete base sat on 3" posts so it's no surprise it needs some attention. I've attached a couple of photos showing the rotten ends of the floorboards and the base is fixed to 3 joists underneath it which are 290mm apart. As I said in my initial post it consists of 21 boards, would it be a case of getting rid of all of the boards affected by the rotten ends or is there a way that just the ends could be removed?

 

What state are the joists and the support posts in?
If they are in good condition I'd replace the floor. You could possibly reuse some of the longer boards at the ends after cutting off the rotten ends and then treating the cut ends with preservative.

 

Dare I say it, it's not a good design.
It's fixable but not straight forward to stop it happening again.
Any new timber required would be better bought from a builders merchants rather than a company which makes sheds or greenhouses.

 

Joists are in pretty good condition a lot better than the support posts which I'm going to replace whilst the base is off the ground

 

Given the questions that you ask, are you willing/able to perform this repair yourself ? If not, get a carpenter to sort it out ; its not rocket science!
If , however, you fancy the reward of completing this yourself, I suggest that you source the replacement timber . as previously suggested above and construct a perimeter to fit the footprint of the floor of the building, in say , this:
Wickes Incised Exterior Grade Timber Joist - 47 x 150mm x 2.4m | Wickes.co.uk
Cut to replicate the angles to create the octogon shape. Consider using these to fix together:

Wickes Jointing Plate - 97 x 35mm - Pack of 4 | Wickes.co.uk


As it is 150 deep, cut back your floor by ,say 75mm , removing any rotted/soft material. treat ALL surfaces, especially the cut ends of grain (2-3 coats) with the product mentioned in my original reply.
Once dry, screw the floor to your new frame created above.
Select treated timber to the thickness of the floor boards to flush the outer area to the vertical sides.Cut and screw this in place. It should be 75mm wide x the floor thickness.
Refix the sides (which hopefully are not rotted as not mentioned to the thicker(47mm) base frame you have constructed.

Ensure the structure is level and free from movement by packing if nesessary. As described by others above , an air gap beneath the floor and supports which do not create ponding will maximise life. Good luck

 

Thanks again for all of your replies, I may well have a go myself and see how it goes. Had you been a 100 mile closer Infradig I'd have offered you the job! Hope you all have a good weekend