Q:what's the best insulation for ceilling for house with semi flat roof?

The pitch of your roof has nothing to do with the kind of insulation you should use. I recommend a fiberglass insulation that is at least 6 inches thick, the more you put in the better.

Q:or in queensland

Depends on whether you are employed or working contract. Currently it could be 18-25 per hr for employee or upto 40 per hr for contract depending on allowances and if you are providing your own vehicle or company vehicle. Then are you doing bats or anticon, it is usually charged on a sqm rate. Call some roofing companies or insulation companies and ask them what their rates are.

Q:As opposed to other roof structures, such as Mansard or Hipped roofs. If so, is it because there is a lesser distance between the internal heat source and the roof?

No, it really does not matter what type of roof as long as the insulation is well done. But of course in a flat roof it is easier to reach all the points with ease whereas in sloping roof some areas may be inaccessible. But, with blow-in insulation that is not a big problem.

Q:I am building a porch roof over an existing patio. The rafters are fabricated I-beams. I plan on putting aluminum soffit under the I-beams. On top of the roof I would like to put down a metal roof. I already put down 3/4" OSB and a rain/ice barrier. Do I need insulation and/or ventilation on top of the rain and ice barrier, or can I get away without it?

Its a outside patio, are you going to enclose it for living space? If not don't bother to insulate and for ventilation there is soffit that comes with vent holes in it. Add; no it will not cause a moisture problem, i had a patio with a open bottom metal roof and had no problems and i live in Florida.

Q:we want to put a model railway up in the loft,and i like the idea of having white plastic cladding throughout up there,my hubby is insulating the roof tomorrow,but he prefers plasterboard,at least the cladding will be maintenance free,

i think it might be able to pass code if you ever sell the house.i myself would use sheets of white wainscoting.also make sure the insulation if it has a paper backing ,paper faces the room.

Q:Would it be worth forwarding the offer to the client? Is the difference that substantial?

You don't want that. If he offers 3.5 instead of the required 3, that is a different story. Otherwise he should give you more material thickness to provide an equivalent R of 3. Yes, the difference can be substantial and I wouldn't forward it to the client. The smaller the R value of the entire roof sandwich the larger the difference it makes. Like the change from 5 mpg to 4 mpg is a 25% worsening in fuel economy, but a change from 100 mpg to 99 mpg is 1%. It will mess up the heating/cooling of the building and the mechanical systems might be inadequate. They could save money on the roof and complain how the building is too hot/too cold or the mechanical systems never shut off and their energy bills are too high.

Q:Why is the most insulation needed in ceilings or roofs? Just wanted to know

well insulation in general is to keep the inside temperature different than the outside. since hot air usually rises, i think it is to keep warm air form escaping in winter. also you don't usually have a heater in the attic, or air conditioning so insulation will keep the air in the attic from having an effect on the air within the house. that is my idea as to why

Q:should thermal insulation ever be applied directly to the underside of a roof top?

Should it be done, No. Thermal Insulation is put direftly above the ceiling. Not on the actually roof top. The reason being, that even though both methods will trap in heat, With the insulation on the arches of the roof, it still allowing heat into the Attic, Or roof space. This means that the top of the roof will infact be the warmest part of the house, and lot of heat will be lost. from the main rooms of the house.

Q:Tax Question: Itemized receipt for roofing and insulation?

Unless this is a rental property, maintenance is NOT deductible. IMPROVEMENTS to your home effect the cost basis used to determine capital gain or loss when the home is sold. As you can excluded up to $250,000 ($500,000 for married filing jointly) of gain the sale of you home, it is unlikely you will see ANY tax benefit.

Q:A roofer who wants to put a new roof on my mobile home says it will dry out. (We live in the rainiest part of the US)

I think everyone is misunderstanding your question. I think what you are saying is that your insulation got wet, becasue of your roof leaking. The roofer wants to replace the roof but not the insulation. If your talking about an insulation board under the roof then I think your roofer is right. Just put a new roof on. If you talking about some kind of fiberglass batt insulation then it probably should be replaced.