Foundation Options For New Garden Room

[gmas2001]

Hi All,

 

I'm planning on building a garden room / workshop on our old veg patch next year and first thing I need to tackle is the foundations. I've attached some pictures of the area below, we're looking at something around 4m wide by 6m long. As you can see the area is on a decline, I have put a rough level on so you can see this. 

 

My debate is what kind of foundations would work best for this project, so any suggestions would be greatly welcomed. I've been looking at a steel bar / square plate pile foundation similar to that used by Oakwood garden rooms on Youtube but I'm sure there are plenty of viable options out there.

 

Thanks,

 

G.

 

 

[gmas2001]

one more pic, areal view of proposed area

[Redbeard]

What's the build? Masonry or timber? If timber I'd do it post and beam and sit each post on a 'Walter Segal-style' pad, which could be anything from a paving slab to a paving slab with lois of concrete/crushed rubble below, depending on ground conditions.

[gmas2001]

1 hour ago, Redbeard said:

What's the build? Masonry or timber? If timber I'd do it post and beam and sit each post on a 'Walter Segal-style' pad, which could be anything from a paving slab to a paving slab with lois of concrete/crushed rubble below, depending on ground conditions.

Thanks for the reply, it's going to be timber frame.

[Redbeard]

Sit it on pads, then, even if it is not post and beam.

 

The copy is not great but have a look at http://www.ianwhite.info/THE_SEGAL_METHOD.pdf for the principle. If you are having stud frames rather than post-and-beam you can just span the pad footings with a horizontal 'foundation timber' situated above the splash-up zone. I have built a lot of Segal-style structures and am a rubbish photographer but I may be able to dig out some pics if that might help.

Edited December 5, 2022 by Redbeard
trypo

[andyscotland]

I'm in the middle of a similar project just now, I used ground screws which has worked really well. No digging at all, just drill a hole then screw them in. And then built a 4x2 timber frame on top to sit the building on.

 

You can get different lengths including ones that can have a section left above ground level, perfect for sloping sites.

 

I got mine from the ground screw centre, and rented their ratchet installation tool - very happy with them!

 

 

[gmas2001]

On 05/12/2022 at 16:42, Redbeard said:

Sit it on pads, then, even if it is not post and beam.

 

The copy is not great but have a look at http://www.ianwhite.info/THE_SEGAL_METHOD.pdf for the principle. If you are having stud frames rather than post-and-beam you can just span the pad footings with a horizontal 'foundation timber' situated above the splash-up zone. I have built a lot of Segal-style structures and am a rubbish photographer but I may be able to dig out some pics if that might help.

Thanks so much for the information, very informative. I'll take a proper look at the article over a cup of coffee this morning.

[gmas2001]

On 05/12/2022 at 19:31, andyscotland said:

I'm in the middle of a similar project just now, I used ground screws which has worked really well. No digging at all, just drill a hole then screw them in. And then built a 4x2 timber frame on top to sit the building on.

 

You can get different lengths including ones that can have a section left above ground level, perfect for sloping sites.

 

I got mine from the ground screw centre, and rented their ratchet installation tool - very happy with them!

 

 

I have started looking at this as an option. How much was it to hire the screw machine? Also roughly all-in cost per screw?

[Nickfromwales]

Same size as I built. I just did 10x concrete pads, rubble full as a foot and concrete on top, then timber ‘legs’ holding a sistered 5x2 ring about 2-7” off the ground ( sloping plot as per yours ). 
Been there a couple of years now, and a little evidence of settlement ( it was on made up ground ) but the 2x 900mm wide fire door blanks I used to make an 1800mm barn door one end still open and close without a whiff of bother, which I’m surprised at tbh.

Biggest regret is a non-insulated roof panel ( powder coated metal clad roof ) and not insulating walls / floors ( as this has a life of 6 years or so before the ground hopefully gets built on ) so didn’t think it worth the expense.

As it’s now my office, I regret not making it much better regardless. It just gets heated by warm air blowers ( fan heaters ) which does heat it quickly, just not cheap!

 

Screw pile option sounds good tbh, and if you want this there for a long time do NOT have any timber in contact with the ground / exposed at that level is my advice. 

[andyscotland]

51 minutes ago, gmas2001 said:

I have started looking at this as an option. How much was it to hire the screw machine? Also roughly all-in cost per screw?

 

I just hired the ratchet tool, so not a "machine" so much as a giant spanner You pay £180 (inc VAT) upfront, then you get £120 back if you return within 21 days - you have to courier it back though and it's heavy so probably works out about £80 to hire. It worked well, you do have to faff a little to make sure the screw is going vertical and it's pretty physical, towards the end of the drive I was having to use my full bodyweight to assist turning it. Though the bar is long enough you could do it with two people if you have someone else handy.

 

Some suppliers rent fancy drills to power them in perfectly vertical but they are expensive.

 

It's also extremely quick/easy to get everything level. Just run a laser line for the tops of the screws, turn the spanner until the line on the outside hits the laser, move on to the next. I got mine all within +/-1mm without any real hassle.

 

I had 22 screws for a 5m x 4m base (could have been 20, but we have a dividing wall in the middle of the building so I chucked a couple of extras on that line just for the sake of it.

 

Including the tool hire, the "Premium" joist brackets, and a chunky SDS drill bit for a pilot hole, it worked out about £47 a screw including VAT and delivery.

 

The only difference I think between standard and Premium brackets is the standard ones are solid plate and you have to use 4 self-drilling screws to fix them together & to the top of the ground screw. The Premium are drilled with slots so you can loosely bolt together with the provided M12s then just tighten up once you have everything adjusted how you want it. It worked out about an extra £2 a screw, but I think that was worth it for the ease of fitting it all together.

 

Probably works out more expensive than rubble/concrete pads, but super quick and in my case it's at the bottom of the garden and the only access is through the house so there was a big advantage in minimising the weight and "dirt factor" of the materials.

 

One last thing, based on a tip on here I ripped up some thin perspex and put a thin piece on each screw between the metal bracket and the bottom of the timber, just to reduce exposure to condensation on the cold metal and hopefully keep the timber nice and dry.

[Russdl]

@gmas2001 Have you seen Ali Dymock's YouTube channel?

 

If not I would thoroughly recommend it. He documents a highly insulated timber frame garden room built from scratch with every detail discussed and explained, it's brilliant stuff.

[gmas2001]

On 07/12/2022 at 15:54, Russdl said:

@gmas2001 Have you seen Ali Dymock's YouTube channel?

 

If not I would thoroughly recommend it. He documents a highly insulated timber frame garden room built from scratch with every detail discussed and explained, it's brilliant stuff.

Interestingly I found his channel today, very informative!

[gmas2001]

On 07/12/2022 at 08:14, andyscotland said:

 

I just hired the ratchet tool, so not a "machine" so much as a giant spanner You pay £180 (inc VAT) upfront, then you get £120 back if you return within 21 days - you have to courier it back though and it's heavy so probably works out about £80 to hire. It worked well, you do have to faff a little to make sure the screw is going vertical and it's pretty physical, towards the end of the drive I was having to use my full bodyweight to assist turning it. Though the bar is long enough you could do it with two people if you have someone else handy.

 

Some suppliers rent fancy drills to power them in perfectly vertical but they are expensive.

 

It's also extremely quick/easy to get everything level. Just run a laser line for the tops of the screws, turn the spanner until the line on the outside hits the laser, move on to the next. I got mine all within +/-1mm without any real hassle.

 

I had 22 screws for a 5m x 4m base (could have been 20, but we have a dividing wall in the middle of the building so I chucked a couple of extras on that line just for the sake of it.

 

Including the tool hire, the "Premium" joist brackets, and a chunky SDS drill bit for a pilot hole, it worked out about £47 a screw including VAT and delivery.

 

The only difference I think between standard and Premium brackets is the standard ones are solid plate and you have to use 4 self-drilling screws to fix them together & to the top of the ground screw. The Premium are drilled with slots so you can loosely bolt together with the provided M12s then just tighten up once you have everything adjusted how you want it. It worked out about an extra £2 a screw, but I think that was worth it for the ease of fitting it all together.

 

Probably works out more expensive than rubble/concrete pads, but super quick and in my case it's at the bottom of the garden and the only access is through the house so there was a big advantage in minimising the weight and "dirt factor" of the materials.

 

One last thing, based on a tip on here I ripped up some thin perspex and put a thin piece on each screw between the metal bracket and the bottom of the timber, just to reduce exposure to condensation on the cold metal and hopefully keep the timber nice and dry.

Thanks so much for such a detailed reply, i'm really considering it as an option now. my concern with any of these foundation options is how high from current ground level the front end of the area is. Something I am considering is digging down at the back end (the right on picture) and building a small retaining wall as to naturally level off the area a little more.

 

 

[Canski]

I’ve watched many of oakwoods videos and he works pretty sleek and efficiently. I’d go with his threaded rod sysrem. I see no flaws in that. In a recent video he said it had worked out 70% cheaper than ground screws. Having said that I just poured strip foundations today for a 5.5 x 3.5 m garden room. I had the luxury of a digger on site though. I know I shouldn’t have poured concrete today but it just turned up. 😀

Edited December 12, 2022 by Canski

[andyscotland]

1 hour ago, gmas2001 said:

Thanks so much for such a detailed reply, i'm really considering it as an option now. my concern with any of these foundation options is how high from current ground level the front end of the area is. Something I am considering is digging down at the back end (the right on picture) and building a small retaining wall as to naturally level off the area a little more.

 

 

 

There was at least one of the companies I found, can't remember which - not groundscrewcentre - that did much longer screws, 1200mm or more, with the idea being you could have quite a long section above ground on a slope.

 

That said levelling a bit might also be a good idea, especially if you plan to put doors on the long or downhill sides?

 

I should also say that my "main" project at the moment is a 6 month extension to the house that is now in year 4. 🤣

 

Therefore part of the deal with my wife for the garden room was that we'd be happy to pay a little bit of a premium for solutions that "just work" so we can complete it and move on.

 

So I didn't do a huge amount of research on more DIY options, I knew concrete was out so just went for ground screws. I can imagine there are ways to do it cheaper with probably not much more hassle but we valued the ability to get a single delivery one day and have the foundations done the next with no need to "pop back to Screwfix for something"!