House building questions

**sheddy** · 19th February 2016, 23:39

Hey team.
I dont really want to build a new house, due to the bureaucracy that will engage. But here in Morrinsville its very hard to buy a house that fits my needs. The Auckland expanse seems to have arrived here as well.Hence considering building. Has anyone recently built a house that sits on top of a concrete garage with back wall as retaining.
Im looking for tips and info help for this "possible " project. My plan is to build a full length block /tilt slab garage say 18m long and around 8-9m deep. Back wall needs to be against a 3m bank. so moisture barrier etc would be needed on back and side walls. Then I'm thinking of putting a transportable home or similar on top of this basement garage. What would be the best way to roof the garage [say 2.4m stud] to support a single story home with a good deck area.
Okay so this is a big garage at least 6 cars and with luck a man cave with good workshop space. 130 M2 transportable homes are in the 250k area. Block basement might cost 100k ???
Can anyone point me in the right direction. Id appreciate it . I need to move my XB12XT on as well as I need to consolidate the toy box.
Thanks

**Akzle** · 20th February 2016, 08:13

pretty basic from a building standpoint.
Ribraft lower slab with sprung blockwall/retaining mulseal and polystyrene is standard+ drainage behind.
Upper floor will either be standard wood floor joists if you can have vertical support across the garage space, engineered clearspan beams, or ribraft again.

**Tazz** · 20th February 2016, 09:21

What he said. ^

Go over kill on the drainage and sealer. It's a bitch digging that shit up again.

**flyingcrocodile46** · 20th February 2016, 09:57

Way too many unknown potential constraints to facilitate economical and relevant advice. i.e, firmly nailing down the "transportable home" parameters (size & shape), percentage of the 18m long front wall of the garage that would be be open (garage doors verses solid wall), the slope of the site (angle of the dangle) etc.

Does the back wall really need to be the retaining wall or could a timber pole retained subfloor space (below a rear wall strip deck) meet your needs? Cheap cladding to close in the base of a pole house with a non load bearing wall framing & concrete floor for non habitable use in conjunction with a timber pole retaining wall would likely be a much more economical way of meeting your needs. As would confining the basement area to the foot print of the upper floor transportable home to avoid complications around the need for waterproof decks etc (though I suspect that size restraints of the transportable home and your desired size and shape of the garaging would likely complicate/compromise the economy and simplicity of that solution).

**eldog** · 20th February 2016, 11:53

Originally Posted by Tazz

What he said. ^

Go over kill on the drainage and sealer. It's a bitch digging that shit up again.

I have seen it everytime someone builds a retaining wall, drainage, drainage, drainage - assume 1000 year floods every 5 years.

The one house I admired for years came onto the market, when I went through it, found I couldn't stand the damp in the lower basement even for a minute.
Every other point of the house was mint, bugger.

If you can put polystyrene under concrete and as a vertical barrier around the outside, it will keep the floor a bit more warmer.

Sounds like a lot of the homes built in the early 70's, house on top of garage.

Make sure you can ventilate it and the stairs are easy going.... for later

Looking for something else for work and came across this below don't know if this suits - they have other flooring suggestions on that site too.

https://atlasconcrete.co.nz/raft-flooring/

**Erelyes** · 20th February 2016, 18:36

Originally Posted by eldog

If you can put polystyrene under concrete and as a vertical barrier around the outside, it will keep the floor a bit more warmer.

Ribraft should pretty much be considered a minimum imo. You can go with Maxraft etc which is a full poly (not just pods) but the cost/benefit wasn't there for us.

Std ribraft is 90mm over the top of the poly blocks. It is relatively inexpensive to increase thickness a bit to say 110mm, which is a good idea especially if you will be having a concrete/tiled floor anywhere.

Perimeter insulation can help. BUT. Before you think about that, think about the design of the house. You should aim to minimise the perimeter/area ratio as much as possible. Ideally you don't have any side of the house which is doubling back on itself. Of course building on top of a garage will also help as the garage is a thermal break.

You can also improve your floor slab insulation by..... increasing your wall thickness. If you go with 140mm framing instead of 90mm, you boost both wall and floor R-value.

Again, cost/benefit wise we didn't find that perimeter insul was worth it. 140 walls were. We were doing a fairly standard flat single story build though.

**eldog** · 20th February 2016, 19:05

Originally Posted by Erelyes

Ribraft should pretty much be considered a minimum imo. You can go with Maxraft etc which is a full poly (not just pods) but the cost/benefit wasn't there for us.

Std ribraft is 90mm over the top of the poly blocks. It is relatively inexpensive to increase thickness a bit to say 110mm, which is a good idea especially if you will be having a concrete/tiled floor anywhere.

Perimeter insulation can help. BUT. Before you think about that, think about the design of the house. You should aim to minimise the perimeter/area ratio as much as possible. Ideally you don't have any side of the house which is doubling back on itself. Of course building on top of a garage will also help as the garage is a thermal break.

You can also improve your floor slab insulation by..... increasing your wall thickness. If you go with 140mm framing instead of 90mm, you boost both wall and floor R-value.

Again, cost/benefit wise we didn't find that perimeter insul was worth it. 140 walls were. We were doing a fairly standard flat single story build though.

nice update, I don't know about the latest trends, just what I saw about 20 years ago on a house I put the underfloor electric heating in concrete slab and what I have seen here and there.

I would suggest as much passive insulation and stuff like you suggested as you can afford, rather than just heating/cooling it after.

Been thinking about putting inverter air con in my current house. Only a thought at present.

**Akzle** · 21st February 2016, 05:35

Originally Posted by Erelyes

Std ribraft is 90mm over the top of the poly blocks. It is relatively inexpensive to increase thickness a bit to say 110mm, which is a good idea especially if you will be having a concrete/tiled floor anywhere.

which jews are doing your floor????

Standard is 4" ribs, 4" raft (slab). I'd be hitting up your council if they're signing off 90mm...

**Akzle** · 21st February 2016, 05:39

Originally Posted by eldog

I would suggest as much passive insulation and stuff like you suggested as you can afford, rather than just heating/cooling it after.

solid advice.
But "passive insulation" isnt really a thing.
You have passive heating/cooling. And thermal mass.

(and insulation. Which isnt actually required if you get the first two right)

which, given he's plonking a relocatable on, isnt really an option.

**eldog** · 21st February 2016, 07:14

Originally Posted by Akzle

solid advice.
But "passive insulation" isnt really a thing.
You have passive heating/cooling. And thermal mass.

(and insulation. Which isnt actually required if you get the first two right)

which, given he's plonking a relocatable on, isnt really an option.

i may have the terminology wrong, but you got my idea.

he suggested using garage as man cave, having spent some time lying on a concrete floor myself, getting the heat losses to a minimum and good ventilation to get rid of damp air is the way to go. Can you insulate a relocatable?

it comes down to cost and what the OP wants, if it's long term better off doing all he can to save later. Most of these temporary ideas turn into long term.....

**Daffyd** · 21st February 2016, 17:49

Originally Posted by eldog

Sounds like a lot of the homes built in the early 70's, house on top of garage.

I had a brother in law in Auckland that did very well out of raising a standard house, building a garage/foundation under it and then lowering said house on to the new garage/foundation. Lives in Seattle now.

**eldog** · 21st February 2016, 20:14

Originally Posted by Daffyd

I had a brother in law in Auckland that did very well out of raising a standard house, building a garage/foundation under it and then lowering said house on to the new garage/foundation. Lives in Seattle now.

Cool
my cusses lived in a house, exactly like these.
i always remember the damp smell in the garage, could have done with a completely sealed block wall, some of the earth wasn't removed and one part only the top half of the wall was sealed. It was a slightly sloping section. Could have done with better ventilation. Always remember climbing and falling down the steep stairs to the house above, slippery as shit in the wet. an internal staircase would have been nice.

good on the OP for thinking outside the square.