Plaster over timber; Unconventional roof: any builders on geekzone?

Forums › Home Workshop DIY › Plaster over timber; Unconventional roof: any builders on geekzone?

Batman

Mad Scientist
29773 posts

Uber Geek

Trusted

Lifetime subscriber

#115506 28-Mar-2013 07:09

Hi I am wondering if anyone knows about leaky home syndrome prevention and leaky roof prevention

There is a property that came across our attention and I'm sure there will be many more so better ask now ...

1) 90s house with brick walls but the roof cavity "wall" is not brick but plaster over plywood bolted onto the timber frame.

My understanding is if there is a way of water getting through the plaster continuously undetected it will then rot the entire timber framing

The tiled roof has no visible flashing and ends 1cm outside the plaster over timber - very good way for water to enter!

So - aucklanders ... what can be done to prevent leaky home syndrome here?

2) 80% of the house is tiled roof. but due to arty farty design the rest of the 'roof' is something that looks like plaster over "rubber" something with a "waterproof membrane" somewhere in there. the proof of the pudding is there is already a leak through it and the owners have poured "bitumen ?tar" over the roof ... is 20% of this house about to collapse?

Thanks for any knowledge (please no opinions only facts and science etc)

NonprayingMantis

6434 posts

Uber Geek

#788343 28-Mar-2013 07:12

The best way to avoid any problems is to not buy it.

Ropata

318 posts

Ultimate Geek
Inactive user

#788347 28-Mar-2013 07:25

Don't buy, simple as that. If there is one leak, there will be multiple.

Batman

Mad Scientist
29773 posts

Uber Geek

Trusted

Lifetime subscriber

#788357 28-Mar-2013 07:57

Not buying it. Just want knowledge. Anyone with knowledge?

wellygary

8345 posts

Uber Geek

#788388 28-Mar-2013 08:54

joker97:
My understanding is if there is a way of water getting through the plaster continuously undetected it will then rot the entire timber framing

Whether the Frame rots when it gets wet depends on a number of factors,

1) What timber is used for the framing? If it just untreated kiln dried pine like the original laserframe then there is the higher possibility of rot, if the framing is treated (H1.2 etc) then it is much less likely to rot

2) What ventilation/gaps exists in the framing cavity to allow water to exit and air to circulate,

The fastest rot will occur in untreated timber with no way for water to drain away or air to circulate,

if you remove one of these then your chance of rotting timber is greatly reduced....

Dairyxox

1594 posts

Uber Geek

#788398 28-Mar-2013 09:10

Im an Architectual Designer, not sure exactly what you want to know from your post however...

How do you prevent leaky house syndrome? Keep the design simple, use known good construction systems & methods. Use licensed building practitioners and master builders. All new homes must have a 10 year warranty. So build new with some confidence.

The specific case you mention sounds like a bit of a nightmare. There is nothing wrong with plywood as a roofing substrate as long as the the rest of the 'system' matches the manufacturers specification or the building code.

I would imagine its got [url]butynol membrane[url=www.ardex.co.nz/products/waterproofing/butynol_roofing] on top of the plywood. Whats important is what happens at the junctions, where the roof planes change (ridges, valleys), where sheets of butanol end, at wall junctions, at penetrations through the roof, there should be nice big overlaps. If its not done properly then its stuffed.

I havent seen plaster on top of a waterproof membrane before, but the idea doesnt sound totally silly, as it would protect it from getting punctured. However it would limit serviceability and obstruct inspection.

Check the plans on file at the council, if anything doesn't match the plans, thats a problem. The plans should also indicate the system used for the roof.

Batman

Mad Scientist
29773 posts

Uber Geek

Trusted

Lifetime subscriber

#788417 28-Mar-2013 09:43

Dairyxox: Im an Architectual Designer, not sure exactly what you want to know from your post however...

How do you prevent leaky house syndrome? Keep the design simple, use known good construction systems & methods. Use licensed building practitioners and master builders. All new homes must have a 10 year warranty. So build new with some confidence.

The specific case you mention sounds like a bit of a nightmare. There is nothing wrong with plywood as a roofing substrate as long as the the rest of the 'system' matches the manufacturers specification or the building code.

I would imagine its got [url]butynol membrane[url=www.ardex.co.nz/products/waterproofing/butynol_roofing] on top of the plywood. Whats important is what happens at the junctions, where the roof planes change (ridges, valleys), where sheets of butanol end, at wall junctions, at penetrations through the roof, there should be nice big overlaps. If its not done properly then its stuffed.

I havent seen plaster on top of a waterproof membrane before, but the idea doesnt sound totally silly, as it would protect it from getting punctured. However it would limit serviceability and obstruct inspection.

Check the plans on file at the council, if anything doesn't match the plans, thats a problem. The plans should also indicate the system used for the roof.

what i'm saying is: if a house has a design prone to leaky home syndrome such as

* plaster over timber with NO cavity *

is there anything you can do to prevent LHS such as

- put something over the plaster to stop leaks
- do something to the top edges of the entire plasterwork (ie plaster-roof) interface

i'm not just asking because i want to buy a house prone to leaky home

i (and perhaps some other geeks) just want to be educated

Batman

Mad Scientist
29773 posts

Uber Geek

Trusted

Lifetime subscriber

#788420 28-Mar-2013 09:46

Dairyxox: There is nothing wrong with plywood as a roofing substrate as long as the the rest of the 'system' matches the manufacturers specification or the building code.

I would imagine its got [url]butynol membrane[url=www.ardex.co.nz/products/waterproofing/butynol_roofing] on top of the plywood. Whats important is what happens at the junctions, where the roof planes change (ridges, valleys), where sheets of butanol end, at wall junctions, at penetrations through the roof, there should be nice big overlaps. If its not done properly then its stuffed.

I havent seen plaster on top of a waterproof membrane before, but the idea doesnt sound totally silly, as it would protect it from getting punctured. However it would limit serviceability and obstruct inspection.

Check the plans on file at the council, if anything doesn't match the plans, thats a problem. The plans should also indicate the system used for the roof.

1) so you're saying if one cannot findout what's underneath the shiny plaster one will never know

2) it's not the roof that has plywood 20% of the roof is a rubber something with waterproof membrane and something else on top like yeah butynol or whatever

it's the wall of the roof cavity that has the plaster over plywood-timberframe

Quic Broadband

Move to New Zealand's best fibre broadband service (affiliate link). Free setup code: R587125ERQ6VE. Note that to use Quic Broadband you must be comfortable with configuring your own router.

ubergeeknz

3344 posts

Uber Geek

Trusted

Vocus

#788422 28-Mar-2013 09:49

Basically the only proper fix for houses with this type of construction is to flatten them and start over.

Building a house which must be built perfectly, and even then can't cope with poor maintenance or a lot of rain, in a place where builders are not experienced with the techniques, people don't generally maintain their homes and it rains pretty much all the time, was a stupid idea. That's why you don't see houses built that way any more, and nobody wants them.

Batman

Mad Scientist
29773 posts

Uber Geek

Trusted

Lifetime subscriber

#788429 28-Mar-2013 09:52

ubergeeknz: and nobody wants them.

that's not true! people will buy most of them :D

people who know will not, but unfortunately i don't think some people know ... coz i see lots of 90s plaster houses sell like hot cakes in the major centres (coz lots of construction in the 90s in the major centres)

Dairyxox

1594 posts

Uber Geek

#788459 28-Mar-2013 10:32

A local design business here that specialises in leaky buildings seems to favor the "huge steel custom flashing" underneath approach. They plan it in 3d and get steel & tube to make it exact.

ubergeeknz

3344 posts

Uber Geek

Trusted

Vocus

#788463 28-Mar-2013 11:00

joker97:
ubergeeknz: and nobody wants them.

that's not true! people will buy most of them :D

people who know will not, but unfortunately i don't think some people know ... coz i see lots of 90s plaster houses sell like hot cakes in the major centres (coz lots of construction in the 90s in the major centres)

They are selling because they are cheap. Any sensible buyer will be knocking them down or simply keeping them as a land investment. The houses are worth nothing if they are indeed "leaky".

Batman

Mad Scientist
29773 posts

Uber Geek

Trusted

Lifetime subscriber

#788472 28-Mar-2013 11:24

how many plaster houses are built in the 90s and early 2000s? (lots because they were cheaper to build - i didnt say cheap, i said cheaper)

how many of them are not currently a leaky home? (probably a very good chunk hasn't been diagnosed as leaky at the moment)

how many people own, sell and hence buy them?

lots!