Shared walls in construction

Alright guys, can any builders or others experienced in building houses from scratch help me out here...

Noticed an increasing number of developments in my area of late are going down the path of having a shared walls in the middle. ie. the two houses on the block are Torrens Title, completely seperate otherwise, but have the garages joined in the middle, and even now some are being built with the rooms of the house having common joined wall in the middle.

Here's a good example. The block has 27.5m frontage and at it's narrowest point in the back it's 15.5m. Council regulations require 8m (and I've seen less) for detached dwellings - so there's plenty of room.

Now I understand this is a good idea if you have limited width to the development block, but I'm now seeing perfectly good blocks with ample frontage like the one above still having the two buildings joined in the middle.

I can only assume this perhaps saves $$ in the building stage? Can anyone give me a rough guesstimate on how much this would save - I realise would be different for every project - but just roughly?

I just can't comprehend why you'd do it when there's no need for it. Surely the small saving you make in the building would be more than equalled (or close enough) to the fact that prospective buyers are now looking at buying a building with a shared wall as opposed to completely stand alone?

Or is there a bigger construction dollar saving involved than I realise?
 
Our PPOR is a semi-detached, we shre garage wll with the neighbours. I cnn't comment on the costs; but there were two reasons the developer made our semi-detached instead of stand alone. 1) because our neighbours have a easement running up the side of their property, which means that although their block is reasonably sized for Canberra (400m2), they had to sit the house on the boundary to fit it in. 2) because our house is the first you see when entering the estate, by putting two joined together you get the illusion that it is a really BIG house, which (apparently) helps with sales, because in reality most of the other blocks are exceedingly small (250m2/300m2 being common).
 
I'm curious too. Something we'd like to work towards if we can is a duplex - common house wall variety, not a shared garage wall. In our council that needs minimum 10m frontage and there is no shortage of infill blocks very slightly more than 20m wide sitting for sale for about $45-55k, which is a LOT better value than buying two 15m wide blocks for $50k each (although now I say that there are 3 very narrow corner blocks for sale privately in one lot with no price just around the corner that might be better value).

I was also figuring that one attached house would be cheaper than two detached ones.

ETA: 15m here is the minimum for a detached house. 10m is the minimum for an attached one.
 
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Steve, the downside far outways any cost saving I would have thought.
Why would anyone want to make a decent house look like a duplex is beyond me. The example you attached above they had to to allow the double garages and I can't say I have seen it doen where it could be avoided.

Andrew
 
Andrew, agree with your thoughts about cost saving vs value destruction.

But that's just it, this is where I can't understand the reasoning. The example above had frontage of 27m - in the area you only need 12.5m per property frontage for double garage blocks. Technically as the block is getting narrower, the end of the garage would probably have the combined width of 22m at that point, but I don't think that would be an issue as council used to let 10m blocks have dble gge's, they changed their rules for the aesthetics, not so much the set out of the buildings - so street frontage was their concern.

Here's another example of what I mean - these two have 8.8m frontages (again only need 8 for detached). Why would you do that instead of these ones a few streets away? The ones on Collins only have frontages of 8.2m, so less width but a better result (imo).

So I still wonder why one would go attached?
 
common walls allow you to build more houses on a lot where there would normally be allowed.

it's referred to in WA as a "build strata" scenario - basically, you HAVE to build them the way planning have agreed to before a title will be issued which allows them to be sold.

otherwise, you could just cut any old lot up any which way, regardless of local development control policy and onsell to someone without the knowledge or appreciation for what is needed to make these types of lots work from a planning and development POV.

hope this helps.
 
Understand what you're saying BC. Makes sense too - you mean so some poor guy doesn't buy a block that is impossible to be built on?

Any thought as to why they would join a wall when they don't have to though? eg. these lots could be sold off seperately at 8m widths and held to build on with plans approved later (ie. no building plans submitted yet) and there would be no problems.
 
I think they might be doing this to follow the guide lines, to have the homes joined like a duplex because this is the only way they allowed this type of construction, on the site, ie two homes, but they have joined them from the garage being CLASS 10 construction rather than from the house being a CLASS 1 construction , being residential, a common wall becomes expensive if it must meet fire, and sound ratings, ? just a half educated guess really, :)
 
Now you've really thrown me through a hoop Craig! If a shared wall is potentially more expensive (or at least not cheaper) then I'm totally at a loss to explain it! :confused:

Just to clarify again, I don't believe it's anything to do with council/zoning/planning regulations etc. I believe it's the developers choice to be building attached rather than detached. eg. No. 24 here is attached, no 18 three doors down are building detached.

Could it perhaps just be the builders offering the attached dwellings are selling these cheaper than detached versions for some reason or another?
 
the zoning might be an issue ?? if its not as you say it may have somthing to do with the land size,( plot ratio ) and adding the common wall saves , for eg 1.2 meters beetween the two units, did you undr stand about the cost involved in a class 1 and a class 10 structure??? ie common walls,
 
the zoning might be an issue ?? if its not as you say it may have somthing to do with the land size,( plot ratio ) and adding the common wall saves , for eg 1.2 meters beetween the two units, did you undr stand about the cost involved in a class 1 and a class 10 structure??? ie common walls,

I think so? Class 10 means they are only joined by a common wall in the garage, Class 1 means they are joined by a common wall running through other areas of the houses eg. bedrooms or living areas. The class 10's are definitely more common than 1's in the area. Whole suburb - with the exception of the fringes along the main roads - has the same zoning.

The land sizes on the two blocks in my last example are the same eg. both 9.6m x 44.6m, one pair detached the other not.
 
yep , but the class 1 common wall is very common, HUH! but dearer to build due to the fire rating required and insulation , but a class 10, this is not required as much, ?? this is all i can offer??? sorry but i hope i helped, :eek:
 
You did help Craig - you answered another question I had about why the garage walls are often shared, but not the rest of the houses. Thanks :)

I still need to find out why people are building duplexes (if you would call it that) at all as opposed to 2 separate dwellings, with all regulations being equal.
 
yeah i think craigb hit it on the head - setbacks on an 8m lot would be a killer.

imagine 1.0 to one side, 1.0 to the other would leave 6.0 of house.

also you can build wall to wall without "sharing" a wall - ie have a pair of cavity brick walls abutting each other - basically you could demo one without affecting the other.

this may be what you're seeing...?
 
yeah i think craigb hit it on the head - setbacks on an 8m lot would be a killer.

imagine 1.0 to one side, 1.0 to the other would leave 6.0 of house.

also you can build wall to wall without "sharing" a wall - ie have a pair of cavity brick walls abutting each other - basically you could demo one without affecting the other.

this may be what you're seeing...?

Yeah you're right - a lot have their own two walls, just touching each other, but still have their own roofs etc so could be torn down individually. Only recently have I started seeing shared roofs etc to make them officially duplexes.

You're right about it being tight though with 8m width. That's a good reason to join if it gives them extra width to work with. Smallest I've seen so far are these with only 6.9m frontage :eek:. I could almost fit 6 of these on my land!
 
a shared roof would just require a 60/60/60 firewall to the underside of the roof material, or projecting through it like a "parapet" wall, ala the victorian townhouses.

i have a transportable module - 2 storey funnily enough - to fit a 4.2 x 14.4 pre-stressed conc slab.

anything is possible - but that corconda street example is just plain freaking horrible.

here's my 7.5m version....these are cavity wall to cavity wall.
 

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yes BC the old 60/60/60 go on somone ask what this means, :D or even the 30/60/90, its a beauty, ;) Blue card would love to tell the class, rather interesting,
 
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