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Let's Try That One Again.

Posted by Crofter , 04 December 2014 · 1,594 views

Firstly, a big thanks to everybody who contributed to and responded to my first blog post. I have had a lot of things to mull over and it was clear that my design needed some tweaking before I submit the drawings to the planners.

So I present design number 8 (!) which borrows a few things from its predecessors. In summary:
- Porch is gone. Storage relocated to a 'utility cupboard' in the hallway which would house the washing machine, hoover, etc.
- Bathroom can be accessed from hallway, as shown, but a Jack-and-Jill or en-suite arrangement are also possible.
- Footprint of the building is slightly lengthened, but overall remains at the 50m2 mark, with about 40m2 internal.
- Walls now baselined as 350mm thickness.
- Patio door and the two small windows have been widened, whilst porch window is gone altogether; increase of about 8% glazed area.

Construction remains similar, with steel piers supporting a timber ring beam, 300mm I-beams for joists and rafters, timber cladding etc. However the walls have been simplified, using a 150mm stud with IWI, rather than the larsen-truss I had originally planned.

Using Thermal Calc Online, I get u-values of around:
floor- 0.14
roof- 0.13
walls- 0.17

I have some room to improve the performance of the walls if I can substute batts with PIR, which depends on budget. I could also improve overall performance by reducing the glazed area to previous levels.

As before, I'm very keen to get thoughts on this before I submit plans. Need to get the planning application in soon though...

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That looks good to me.


When you submit your planning, make no mention of the "portable building" aspect. They just want to know what size and shape, what it looks like, external finishes used etc. It's only building control that need to know it's a portable building.

I'm still not entirely sure about your steel beams idea. Yes it will work, but if you ever had to move it, it would require high precision to get the new set of steel beams spaced just right. I would still think more along the lines of concrete columns with flat tops for the ring beam to sit on, and then tie down straps to keep it there when it blows a hoolie.

My neighbour has done a bit more on his. The area under the house he has now covered in plastic sheet and then a layer of gravel. I assume that's how the space under the house will remain.
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The steel beams idea was about thinking of a bombproof way of stopping it from blowing away. I havent't fully costed out the steel of course- concrete would probably be cheaper.
In theory, the timber ring beam could sit on a variety of support options, either now or in the event of a future move.

Interesting to hear about your neighbour's progress- remember to keep me updated :) I had wondered about what to do under the house, his approach sounds very sensible.
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I'll take another picture and post it, sort of an unofficial "neighbours build blog"

When they start building the actual house, which I don't think will be until the spring, I'll see how they strap it down.
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I've put another entry and picture in your thread on the forum http://www.ebuild.co...385#entry103385
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I still think the idea of a sheltered porch or mini conservatory entrance that is outside the thermal envelope of the house is a good one. Even if it is just a sheltered area to take your boot and outdoor clothes off before you go inside. It will give you some extra space albeit cool and could be treated as sort of a utility room. It will also act as an airlock for entering the house and help keep it warm. If it is outside the thermal shell, it could literally just be butt joined onto the side elevation. Just a thought.

And I know it late to say this but what are the advantage of the steel beams over straight concrete pads? If you bolt the frame down to such pads, it isn't going to anywhere in a hurry.
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Yes I can see a porch going on later, assuming I get usual PD. I did play around with some layouts where a porch went on the gable (thereby keeping the building within portable building dimensions) but I didn't like how the space worked, or how the building looked. So thought I'd just get rid of it (for now).

A glance at the cost of steel has me considering other options. I could simply cast piers in-situ with galvanised tie-down strapping embedded in the concrete, or alternatively rely on bolted fittings, which I am not so sure about given the winds up here.
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If you do the calcs, I think that you will see that the frame will burst apart long before a set of heavy bolts shear. If the wind gets that bad you'll be left with shards rather than a house in Oz (the one where the wizards live rather than the descendants of our petty criminals).
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Crofter what is your budget for the build and how much work are you planning on doing yourself? I think I remember you saying you are doing this as a holiday let business? I'm hoping to achieve something similar on a sloping site I've just purchased. Trying to decide whether my budget will stretch to 3 bedrooms instead of two so interested on your costings!

Thanks
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My attempt at a complete costing currently stands at £33k. This is just materials, the only outside labour of any sort is the plant hire for the access and drainage. I'm planning to do virtually everything myself- I only work for six months of the year so need to do something useful with my time (or so the wife says...)
My cost breakdown at the moment is:
Total: £33,211.00
Fees £501
Services £3,300
Drainage £7,784
Access £4,380
Founds £675
House £6,423
Insulation £1,654
Windows £2,295
Interior £5,284
Wiring/Plumbing £915

There are, of necessity, some very significant guesses in there! There is also little, if any, allowance for incidentals like nails, screws, and other sundries. Most prices for materials have come from phoning a couple of builders merchants locally, so hopefully there will be some savings to be made by buying in bulk, which might offset the inevitable rises and items I will have forgotten.

'House' means the timber frame, cladding, roofing, internal linings and partitions.
Insulation I have budgetted separately just so I can see the numbers at a glance if I change the spec.
'Interior' covers the internal doors, fitted kitchen/bathroom items, MVHR, and the woodburner.

It wouldn't cost very much more to do a bigger house- the basic fabric of the build is cheap. As a conventional project, I could be accused of under-developing the site. However, I have had feedback from letting agencies who suggested that there wasn't much to be gained from a second bedroom. The couples market is strong, and is all year round. Families are more often looking for budget options and are restricted by school holiday dates. So the plan is to market to couples, especially the retirees who might appreciate a place without stairs (letting agent's words, not mine!)

In the event that my plans change, the gable wall off the kitchen would accomodate an extension, and the house is sited on the plot so that there is space to do this. But at the moment the most sensible thing to do is to get the house on the letting market as quickly as possible within the budget that I have.
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