Insulation

[groeneaj]

G'day,

I have a metal roof with only sarking on the slope of the roof. The ridge of the roof has blown in insulation, but it still gets ridiculously hot upstairs during summer to the point where air conditioning is almost useless.

The house is two story with double brick construction. Downstairs is really cool in summer, but I need to insulate the roof, especially now that my daughters room is upstairs.

Below is a picture of where I'd like to put insulation. I have good access to the east side of the house where I can push the insulation up with a stick. The west side is a little bit more difficult as the ducted air conditioning is in there. But I can still navigate my way around it.

My question is, what do you recommend I use? I've done some research but the different choices gets confusing. Has anyone got experience in doing this, and if so, what product did you use? I don't mind spending a little extra if it means I'll get good results.

I can measure the opening tonight if that helps.

Thank you

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[Mr Brush]

Andy,

Not sure if this is applicable in your situation, but they use this stuff a lot in the UK for insulation in wall cavities for double-brick houses.

Foam Insulation Services For Home & Commercial Premises

It might be easier to get this into hard to reach spots?

[Bohdan]

Another solution is to fit ventilation to the roof (like a fan) to lower the temperature and put the insulation on the ceiling.

[groeneaj]

Another solution is to fit ventilation to the roof (like a fan) to lower the temperature and put the insulation on the ceiling.

Good point, I actually meant to include this in my original post. I was thinking of getting some whirlybirds installed to circulate the air. I'll do some calling around and see what I come up with.

[groeneaj]

Andy,

Not sure if this is applicable in your situation, but they use this stuff a lot in the UK for insulation in wall cavities for double-brick houses.

Foam Insulation Services For Home & Commercial Premises

It might be easier to get this into hard to reach spots?

I really like the idea of spray insulation and I ran this past the wife a while back. She wasn't a huge fan of the chemicals, especially now we have a little one. They recommend you stay out of the house for a while whilst it's being sprayed.

[NCArcher]

I like the look of this stuff. Watch the video, it's quite good.
Earthwool Ceiling Batts | Knauf Insulation

[ian]

Here, a gap like that would be insulated with rigid foam up to 4" thick, but that would be overkill in the lower mountains.

My recommendation is fiberglass bats in the ceiling -- remember to wear protective / disposable clothing and mask and eye protection when installing it -- plus install whirlybirds and breather holes to exhaust the hot air in summer.

When installing the insulation make sure you don't cover any down lights or in ceiling light fixtures, or other heat sources.

[Bohdan]

She wasn't a huge fan of the chemicals, especially now we have a little one. They recommend you stay out of the house for a while whilst it's being sprayed.

And for several days after while the chemicals cure.

[groeneaj]

I'm liking the earthwool insulation that Tony posted. Do I need a gap to let it breathe or do I just stuff it in there?

[Fuzzie]

That doesn't look like a gable roof over a flat ceiling. I assume the ceiling is raked inside? In that case I would think any blown in insulation would be fighting gravity to stay in place. How much stuff is actually on top of your roof? Would it be possible to take the metal off, redo the sarking with insulated stuff and put the sheets back?

Is all the heat actually coming from the roof? Does the ceiling feel hot on the inside radiating down? Are there big north facing glass areas or west walls that are capturing the heat?

[cava]

According to the Alternate Technology Association, whirlybirds do not work as effectively as claimed.

[bueller]

Thanks for the info cava, about to fit ventilation to the shed and had planned to get a whirlybird but not anymore. Read this post below which seemed like good info, will need to confirm with some secondary sources though.

Roof Ventilation Alternatives Chart - Roof Ventilation Blog

[ian]

Going back to Andy's initial post, it looks like he has Gyprock attached one side of his rafters and the roof purlins the other.

I'm not sure that any of the insulation products discussed are designed for that situation. As far as I know, ceiling insulation is designed to provide a thermal barrier between the roof cavity and the living areas. And to be fully effective the roof cavity needs to be able to exhaust the hot air generated inside the roof from solar radiation to the outside, with replacement air drawn from the under the eaves where the air is typically cooler.

I also understand that it is important to maintain an air gap between the insulation and the roof -- otherwise you get thermal coupling with the hot roof which conducts the heat into the ceiling material.

Perhaps Andy's most effective insulation will be to ventilate the roof cavity, so that the air heated through contact with the very hot roof is exhausted outside the house and replaced with cooler air drawn from the shady side of the building. A forced air flow coupled with 25 to 50 mm of rigid foam insulation might do the trick.

The other option worth investigating is installing a sprayer to wet the roof on very hot days. When I lived in Broken Hill the workshop was fitted with a lawn type sprayer system which sprayed water onto the roof on very hot days. The cooling effect of the evaporation reduced the heat radiating from the iron into the building.

[groeneaj]

I'll take some more photos tonight when I get home which will explain the layout a bit better.

[groeneaj]

Hopefully these pics give you more of an understanding of the layout of my house.

I was thinking batts or similar in the roof line and walls (west side has no wall insulation upstairs), then some sort of exhaust fan or whirlybird to remove the hot air. Maybe even eave vents also.

Side of house (north facing). There is a vent there but it ain't doing much.

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East side of house

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Here you can see the roof line is followed on either side. The flat area has blown in insulation. I couldn't tell you how much unless I go up there and have a look.

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This is the inside of one of the walls. The plan was for the person doing the blow in insulation was to cover the ends with batts, then blown in from the outside by taking the roof off. Long story short, they didn't end up doing it. This side has batts in the walls, the west side doesn't so I'll need to put wall batts in there also. The gap is where I took a pic in my first post.

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