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My Garden Room Build - 9m x 4m

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robgul

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I know what you mean about trellis and off-the-shelf fencing etc - I've just fenced the whole of our garden with horizontal slats about 12mm apart - the timber is just roof batten stapled onto the uprights (with the neighbour's lap fence behind) Very pleased with the effect.

DSC01418.JPG
 

Molynoox

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That looks really good Rob 👍 cool idea.

Looks like you are running a mini restaurant with all those tables; how much for steak and chips?
Martin
 

robgul

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That looks really good Rob 👍 cool idea.

Looks like you are running a mini restaurant with all those tables; how much for steak and chips?
Martin
:) - yep, it did look a bit like that with the tables - the patio had only just been laid and we just got all the furniture out.

The fence idea also looks pretty good when it's painted - this is at the front of the house, stained with Cuprinol Garden Shades Ash Black

DSC01073.JPG
 

flying haggis

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If you went with an angled pergola, I would "hang " the end from under the roof overhang instead of having the post in front of the building in the way of the door. Does that make sense?
 

Molynoox

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:) - yep, it did look a bit like that with the tables - the patio had only just been laid and we just got all the furniture out.

The fence idea also looks pretty good when it's painted - this is at the front of the house, stained with Cuprinol Garden Shades Ash Black

View attachment 122355
looks brilliant, nice idea, and nicely done too (y)
 

Molynoox

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If you went with an angled pergola, I would "hang " the end from under the roof overhang instead of having the post in front of the building in the way of the door. Does that make sense?
that's a smart approach, I like it.
the only potential issue is that the height of the pergola spars are then a little constrained by the specifics of the building design but they are at similar heights so probably not a problem

I remembered another deciding factor for straight design too; I believe I was struggling to get Cedar in lengths longer than about 2.5m, so that made it tricky to get the long diagonals sorted. I think needing those lengths pushed me towards more expensive Cedar suppliers and that helped me decide to go 'straight'.
Martin
 

clive griffiths

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I know what you mean about trellis and off-the-shelf fencing etc - I've just fenced the whole of our garden with horizontal slats about 12mm apart - the timber is just roof batten stapled onto the uprights (with the neighbour's lap fence behind) Very pleased with the effect.

View attachment 122352
Hi Rob.
What is the paving you have.

Clive.
 

robgul

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Hi Rob.
What is the paving you have.

Clive.
It's black sawn limestone in 600 x 900 size - that has been sealed with Stonecare colour enhancer (probably need re-doing every couple of years) The wall cladding is Thermowood fixed on batten attached to a blockwork wall
 

Molynoox

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Aug 2021 - Rain Drain and Decking Prep

Rainwater
I needed a solution for rainwater coming off the roof, guttering is the standard method, the question is where to route the water to.

Option 1: Soakaway
Downsides: no idea how to build a soakaway

Option 2: Tap into drain
Downsides: no idea how to tap into a drain

Anyway, there was a drain very nearby that took rainwater from a garage roof so once I excavated a bit I noticed that there was a T junction that looked pretty easy to tap into.
I also measured the fall between the T junction and my expected gutter exit at floor level and it was over '1 in 40' so this looked like a good option and I proceeded to ignore the soakaway idea.

Method
I picked up a few parts from screwfix, some waste pipe, some 90 degree angles, a flexible coupler (because there was slight kink to deal with) and a little rubber thing that goes from waste pipe diameter into drainage pipe diameter.

Pretty straight forward to install - dig a trench, connect the parts up, lay it on soft ground pea shingle in most places, then back fill with soft ground (no rocks or stones).

IMG_20210814_130222.jpg

IMG_20210814_130213.jpg

It doesn't look it but the ground is sloping towards the drain
IMG_20210815_140453.jpg

IMG_20210815_140503.jpg

IMG_20210815_150203.jpg


The next day I had another go at this as I realised that the end of the pipe sticking up out of the ground was visible when viewing garden room from the front at certain angles. So I moved this part further down the side wall which meant getting more parts:
1. longer pipe to extend the distance
2. replacement 90 degree bend because removing the original with a hammer turned out to be a terrible idea - those things really disintegrate!

Decking Ground Prep
At this stage I also got the levels sorted to accept the decking.
I'm planning on using those adjustable plastic plinths that all the decking companies seem to sell - they seem like a nice solution but time will tell. The building is raised above ground level on the right hand side, but not so much on the left hand side (50mm on left and 250mm on right). The timber decking base is 100mm thick which meant it would need to sit 50mm below ground level. But I didn't want the base of the left hand side sitting on the ground, I wanted to ensure it was raised up out of the way of water / moisture sittin on the plastic pedestals . Therefore I needed to dig down a bit on the left in order to have the deck supported at the right height. I also wanted a reasonably flat and solid platform to put the pedestals on. I considered putting down hardcore but decided just to compress the ground with a tamper to create a solid base.

Pedestals
I found out the smallest pedestal size and dug down enough to accomodate both the pedestal and the timber frame (plus a bit of wiggle room). The pedestals come in lots of different sizes from about 30mm up to about 300mm (in fact I think they can be stacked and go even higher, even up to metre or so I'm thinking but you will need to check that). The ones I bought were I think called Rhinodeck or something but there are loads of suppliers for these things. Anyway, they each have a range, for example 50-70mm, or 200-300mm and you have to buy the right ones for your application, and it isn't all that straight forward to work out what you need :)
IMG_20210814_151534.jpg

Notice the pile of dirt in this picture that I will 'deal with later'. Turns out 'later' is a time, far, far into the future....
IMG_20210814_155722.jpg

Levels and parts ordering
So once it got a bit darker outside, I set up a laser level pointed at the height on the outside wall where the bottom of the timber deck frame would be (this is the same level as the top of the pedestals, obviously). Then I went around with a tape measure on every location of the pedestals and wherever the laser intersected the tape, I noted the measurement and wrote it down. I think I spaced mine every 500mm, they are rated at over a ton each, so the loading wasn't an issue, just span, and with a 100mm x 50mm timber for the base, spanning 0.5m across the supports is not an issue in the slightest.
IMG_20210814_202751.jpg

Here is the 'document' I created telling me the required heights for the individual pedestals.
Once I had the heights I created a simple table of the exact parts I needed and quantities of each and then I went online and ordered them. What could possibly go wrong.
IMG_20210814_213104.jpg

Here are the parts as they arrived, some assembly is required and it isn't as straight forward as I would have liked to assemble them. The assembly takes seconds for each one, but knowing which parts to put together is the slightly tricky part as you have not only different base heights, but also different 'stalk' heights. I had to go on the website and figure out which parts to mate with which other parts in order to build up the actual parts I ordered. I mentioned to rhinodeck that this was harder than it needed to be and they agreed and planned to sort something out better for next time, like a simple chart that comes in the box, rather than just the puzzle pieces.
IMG_20210817_102052.jpg


Martin
 
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Molynoox

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Aug 2021 - Decking Base

I thought this was going to be really straight forward, having just constructed an entire building using what I though would be the exact same techniques. The curveball came in the way of the diagonal area. Defo some mistakes made here, and plenty of good learning.

I made a sketch of the basic design of the timber base, but this turned out to be a problematic design.
IMG_20210814_180021.jpg

In future I would do the following:
  • Use subframes and bolt them all together as you go (this is what I did for the most part, but not when I got to the really complex diagonal section - no, I decided to make that part really hard instead)
  • make as much of the base as possible using square or rectangular frames, and then finally add in whatever extra necessary to make up the diagonal part or parts.
  • make sure that each subframe is a reasonable size and is 'self supporting' meaning that it wasn't reliant on some other subframe for its structural integrity.
  • Do NOT make one massive diagonal component that ends up being a bit of a nightmare to manipulate into place and mate up to the rest of the structure.
  • Ensure you have timber that is long enough for the longest side of your longest sub frames, rather than having to join two timbers together
  • Think about how to get the joists fixed if building a 'perimeter frame' first
So in a nutshell, I made a similar mistake as with my base for the main building when I built the 'perimeter frame' first to ensure it was all the perfect size and shape, and then built the interior structure (sub frames + joists) afterwards. This was an ok idea in theory but I didn't plan the subframes and how I was going to get the joists attached to them without toenailing.

Decking boards
A final mistake I made was not thinking ahead enough about the composite decking planks and exactly where they were going to fall and how I was going to attach them. I did space the joists at consistent 400mm centres, which I though would be fine, like it is with sheathing OSB, plasterboard etc, and it was fine for the straight sections, but its not quite that simple when you get to the diagonal parts. The main reason for this is because I have a 'picture frame' design on the decking which means that the edge board uses the edge of the timber frame for support and you then need additional supports putting in to support the ends of the interior planks (because the edge boards are covering up the edges of the timber frame so you cant attach to that). That probably makes no sense so I will move on.
In fact here is a picture from the future showing the 'picture frame'
decking picture frame.jpeg

Anyway, I will cover laying the composite decking later, and talk at that point about how I upgraded my base to neutralise the problems just mentioned.

Decking Selection
When I built the frame, I had already selected the composite decking product as I needed to know the exact thickness of the boards so I could get the threshold perfect (i.e. flush). My boards are 22mm so I needed the frame to sit 22mm below the door threshold.

I received samples from 7 different suppliers then put them all into a selection matrix so I could chose (considering factors such as cost, look, quality). In the end I got the shortlist down to 3 or 4 suppliers and 5 or 6 different products, all in a grey/anthracite colour to match the doors.
IMG_20210920_153623.jpg

Here is the shortlist of 6 products once I had filtered out the wrong colour, poor quality or mega expensive ones
decking boards shortlist.jpeg

One column I would add in the future to my selection table would be the clips / fixing method, this turned out to be quite important, but I will cover the details of that later.

Decking Frame
IMG_20210816_180544.jpg

Here you can see how I have cut off the edges of the pedestals which are close to the edge of the frame - this is because I wanted the pedestals supporting the bearers and not just the joists and if you have them under the bearers then they protrude out from the frame
IMG_20210818_165926.jpg

IMG_20210902_122126.jpg

Waterproofing
I applied some roofing paint to the tops of the structure. I know that people have had 15 years out of unprotected tanalised timber bases but I figured that waterproofing the tops of the joists where the water might sit will add another 10 years or so on top of that. I did consider joist tape but its crazy expensive compared to the roofing paint option.
Note: I do use the tape in the end, but again I will cover that later,,,,
IMG_20210917_124005.jpg

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Fixing the base to building
I considered having the base entirely floating because I didn't want any water running off the decking towards the building, but in the end I decided that fixing it to the building would add a lot of stability and would make it feel a lot more solid. Also, I managed to come up with some ways mitigated the risks:
  1. I have a gradual fall on my decking base that runs away from the building (its about 1 in 30 and it look completely flat unless you get your spirit level out - this is actually normal best practice on decking bases)
  2. I have created some weird flanges that bridge the gap between the building and the base, that allow the water to run off safely
  3. I have house wrap covering the building, right down to the bottom
  4. I have used roofing paint on the bottom 200mm of the house wrap
Here are the weird flange things which I made from some plastic trims, screwed together back to back so that water runs away from the building on one side and away from the timber base on the other. This also adds a 20mm gap in between the timber frame and the garden room. In the future I would avoid the faff of making these and try and find something off the shelf like a 20mm cyclindrical spacer that would allow you to screw the base tight to the building but at same time create an air gap for safe water run off.

IMG_20210917_170929.jpg


Martin
 
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eribaMotters

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I'm not sure that you are allowed to divert your rainwater into an existing drain. Whilst the workshop structure is exempt from planning regs the rainwater issue is not. I believe up to 6m2 of roof area is exempt and in the case of a previous garage extension I completed, that had to abide by building regs, the water dispersal was not covered and I was allowed to let it run down the drive and into the road.

Colin
 

Molynoox

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Cheers Colin, that's good info.
I did actually have a plumber round to look at this and he advised the drain method I showed above. Looks like I might need to look into this a little more, thanks for making me aware of the details 👍
 

flying haggis

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just look on your roof rainwater runoff into the drain as helping to keep the sewers flushed clean.......... (its where my workshop roof rainwater went..)
 

Molynoox

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just look on your roof rainwater runoff into the drain as helping to keep the sewers flushed clean.......... (its where my workshop roof rainwater went..)
Some of the rules around these things do seem a little strange - often when you look into it you realise the rationale behind it, and at other times it doesn't make any more sense no matter how hard you look into it. Not sure where this one sits :)
 

Molynoox

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I'm not sure that you are allowed to divert your rainwater into an existing drain. Whilst the workshop structure is exempt from planning regs the rainwater issue is not. I believe up to 6m2 of roof area is exempt and in the case of a previous garage extension I completed, that had to abide by building regs, the water dispersal was not covered and I was allowed to let it run down the drive and into the road.

Colin
I have now taken a read through Building Regulation Part H, specifically section H3 concerning rainwater drainage, and I see no mention of the 6m2 constraint you mention. The best guidance I could find is as follows:

Building Regs Part H3 introduction.jpg


Building Regs Part H3 guidance.jpg


So this mentions that rainwater drainage requirements are satisfied if the gutters are up to scratch and can handle the rainflow and if the rainwater discharges to a soakaway or surface water drain or sewer. Which mine does.

I have no doubt you didn't imagine the 6m2 constraint but I cant find any mention of it anyway, and would appreciate your help to provide reference to the regulation.

Martin
 

eribaMotters

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You are in look. It was some time ago, back in 2000, I extended the front of the garage and was able to use the 6m2 rule that was applicable in Essex. Time moves on and we are now on Merseyside and I've had to adapt to regional differences. Don't get me going on footings, but is is suffice to say it's a dam site easier up here on sand than Essex clay.

Colin
 

Lazurus

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I have just added a 40m2 workshop and I had to install a 1m3 soakaway 5m away from footing and 2.5m away from boundary. I used soakaway crates I could have broken into the garage downpipe and exit but as this was possibly also a soakaway I decided to put a separate one for the workshop as it would be much harder to do this retrospectively if the existing soakaway was overwhelmed. Around here adding rainwater to foul water is a big NONO and carries quite a penalty, certainly more than a soakaway costs.
 

Molynoox

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I have just added a 40m2 workshop and I had to install a 1m3 soakaway 5m away from footing and 2.5m away from boundary. I used soakaway crates I could have broken into the garage downpipe and exit but as this was possibly also a soakaway I decided to put a separate one for the workshop as it would be much harder to do this retrospectively if the existing soakaway was overwhelmed. Around here adding rainwater to foul water is a big NONO and carries quite a penalty, certainly more than a soakaway costs.
that's good info, but where / how is this regulated? Is it written down anywhere?
thanks
Martin
 

Lazurus

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that's good info, but where / how is this regulated? Is it written down anywhere?
thanks
Martin
I did a few google searches of various suppliers and installers and they all gave the same guidelines - its in the NHBC riles and regs as below



5.3.11 Surface water soakaways - NHBC Standards
https://nhbc-standards.co.uk › 5-3-11-surface-water-soa...




Soakaways should be: · built on land lower than, or sloping away from, buildings · sited at least 5m from the foundations of a building · sited to take account of ...
 

Molynoox

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thanks, some good info inside that standard, and I will certainly take a read (y)
Putting aside what is best practice (I don't question any of whats being defined in that document) - I have a query specifically about the legality of what you are building (you mentioned a penalty being issued in your area) - I am a little confused here, I thought building regs was the standard which defines if you are building things right and hence defines if you will (or not) receive penalties for doing it wrong?
Are there other standards that you are legally required to comply with?
I hope that doesn't sound argumentative, I just want to understand it.
Martin
 
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