blocking up underfloor ventilation

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Re: blocking up underfloor ventilation

Postby Cherokee Solar » Fri Jul 13, 2012 10:10 am

Hi you lot,

I can speak on this subject from experience, being an owner builder with many projects under my belt, unlike most of you arm chair theorists. ;)

a) It is worthwhile packing insulation under your timber floor. The results here speak for themselves. The timber floors here are never too cold or too hot.

b) Concrete slabs are the preferred building method for the construction industry as they require little skill to set out and build and more importantly they are quick. A concrete slab takes about 2 days from commencement to completion, whereas stumps, bearers and joists can take several weeks to a month and require a lot of skill to get just right.

c) If the average ground temperature is 24 degrees, why would you want that temperature being radiated into your house on an already hot day? During winter, haven't you ever noticed that tiles over concrete slabs radiate cold air into an already cold house.

If you still don't believe me, go outside and sit on the ground - over winter - and see how long you can do this and then remember that your concrete slab has to perform this very function, 24/7, 365 days per year.

As to insulation in slabs, remember that concrete has quite a bit of thermal mass and conducts temperature quite well, so despite the insulation, it will still settle on the average ground temperature, regardless.

Engineers have a saying that goes something like, "good, quick, cheap - pick any two".

Regards

Chris
Off grid solar + hot water. Heavily insulated + owner built flamezone house BAL-FZ. 300 mixed fruit trees + herbs + flowers + vegetables. Bees + heritage chickens. High up in the mountains north of Melbourne. http://ferngladefarm.blogspot.com.au/
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Re: blocking up underfloor ventilation

Postby munrre » Sat Jul 28, 2012 1:00 pm

Location, location, location.
I was advised by the SA energy information office (now defunct I think) the underfloor insulation was a waste in Adelaide. Which is a good thing because I have a phobia about crawl spaces!

I assumed Perth would be similar but it appears I was wrong.
I found an interesting article using modeling on the subject which has a few contradictions but also mentions the effect of blocking up the underfloor. (or as they call it, minimising the sub floor air flow)
http://www.solarlogic.com.au/profile/Th ... tivity.pdf

The graph below is a comparison to a "base house" with uninsulated slab. So under floor insulation is worth the effort and money in cold areas but can be detrimental in warmer climates.

Image
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Re: blocking up underfloor ventilation

Postby zzsstt » Sat Jul 28, 2012 3:08 pm

munrre wrote:Location, location, location.


Also "design, design, design".

Everything depends whether we are trying to gain heat or lose heat, and how the interior temperature compares to the exterior temperature.

Cherokee Solar wrote:As to insulation in slabs, remember that concrete has quite a bit of thermal mass and conducts temperature quite well, so despite the insulation, it will still settle on the average ground temperature, regardless.


That is assuming the design does not incorporate any usage of the thermal mass. Slab edge insulation can decouple the slab from the rapid daily changes in surface soil temperatures, which means that a correctly designed house can allow winter sun to shine on the slab through the day and store that heat to warm the house at night. Underslab insulation can increase that effect, which may or may not be desirable in any given location based on deep soil temperature and thermal conductivity. In summer the soil below the slab is shaded and therefore doesn't warm up as much as "exposed" soil, so the problem of heat radiating from a hot floor at night are far less might be imagined.

There really is no set answer, it depends on micro-climate and soil type. The thermal resistance (or conductivity, take your pick) of soil varies enormously between soil types, and also with moisture content.

Insulation of suspended floors also depends on design and climate, as shown by the graph posted above.
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Re: blocking up underfloor ventilation

Postby James@GreenStart » Sun Apr 28, 2013 7:21 pm

I'd have to recommend against closing off the ventilation.

As a local Building Surveyor I have seen the damage this can do. Damp, termite etc.

If you want any advice send me an email through my webpage http://www.greenstartconsulting.com.au. Im sure to see that and respond soon as I don't come on here often enough.

Alternatively I think the Australian Building Code Board have a useful publication dealing with condensation http://www.abcb.gov.au/education-events-resources/publications/~/media/Files/Download%20Documents/Education%20and%20Training/Handbooks/2011_CondensationHandbook.ashx

All the best.
James.
Regards,
James
Green Start Consulting
webpage: http://www.GreenStartConsulting.com.au
services: http://greenstartconsulting.com.au/services
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Re: blocking up underfloor ventilation

Postby bazzle » Sun Dec 15, 2013 11:34 am

Im on top of a hill in Ringwood Vic.

I blocked off the vents under my place quite a few years ago and had issues that took a few more years to fix. Mould growth on the soil.

I was chasing the same goal. I ended up getting foam tape and filling every gap under skirting, around windows etc. That made a huge difference at the time. I used a wet finger to chase out the places the draughts were coming from.

I now have sealed double glazed windows and doors to complement the sealed skirtings etc.
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Re: blocking up underfloor ventilation

Postby bazzle » Tue May 27, 2014 1:35 pm

Forgot to say I ended up making "More" vents for under the house to keep it healthy.
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