Insulation?

[kjsayers]

Can you actually have too much insulation in your attic? Is there a number of inches where the effectiveness is maxed out?

 

[Cowboyjg]

The answer to that is yes..... You must have proper ventilation in your attic. Air circulation assists in the insulation process by keeping temperatures moderate and moisture down You can't have soooo much insulation that you infringe on air circulation. Poor air circulation causes condensation. I can't speak to the exact number of inches of insulation required to achieve 0 improvement but based on my years of building homes I would think that after about 12" you don't gain enough to justify the cost of the insulation. I have found this site helpful. Try posting your question there. I think you'll get some good info.

 

[inveresk]

Adding insulation to the attic will certainly cut down on heat loss and so improve the thermal efficiency of the building but there are other elements that contribute to heat loss - windows, doors, walls, ventilators, extract fans, chimneys, etc. There comes a point where little extra benefit accrues from additional insulation in the loft because the total heat losses due to these other elements becomes the major factor driving the thermal performance. Unless these other elements are improved as well, then there comes a point where the cost benefit of adding more insulation doesn't square. Draughts also make a huge difference in thermal performance. A windtight building will perform well in all weathers. A loose fit building will lose a terrific amount of heat in windy conditions.

 

[BobRip]

It never maxes out, but you do reach a point of diminishing returns. Every time you double the insulation you cut the losses in half, but that half is one half of the previous amount saved by doubling. Also you must leave a gap between the insulation and the roof or moisture can build up and rot the roof sheathing.

My wife's cousin bult a house with 4 feet of insulation in the attic in Minnesota. He used passive solar heating, insulated shades on the south facing (and only) widows, and one base board hot water heater that water was pumped to from the hot water heater. The house was also earth burned on three walls.

Bob Rip

 

[inveresk]

Ventilation heat losses can be dealt with by means of a heat recovery ventilation unit. Essentially, this is a heat exchanger which uses the warm, spent air to preheat incoming fresh air. These work and, if fitted correctly, can make a significant contribution to thermal performance.

Condensation shouldn't be a problem in a properly designed building. It's normal to prepare condensation profiles for the different elements of construction at detailed design stage to ensure interstitial condensation is avoided.

 

[inveresk]

It's possible to avoid ventilated roof spaces. Most of the houses I design are "warm roof" houses. By placing the thermal insulation outside the roof sheathing and by using a breathable membrane over it, the dew point is moved outside the zone where condensation can affect the structure. Warm roofs have the benefit of being forgiving - if the ventilated space in a conventional design is blocked by careless workmanship, etc. then you could have problems. Warm roof construction also allows the roof structure to contribute to the thermal mass of the building and allows the same structure to be exposed for additional aesthetic appeal.

 

[heehaw]

a roof is just a slanted wall: if you fill the attic with insulation, all the way to the roof, there is no need for ventilation: is there a return for the bucks, probably not, unless you have a raised/vaulted ceiling, which would require much less insulation.
heehaw

 

[dmccarty]

kjsayers,

In addition to what others have said, if you have AC it should be sized to the specs on the house. Adding more insulation could cause the AC to short cycle. The cost on running AC and I think this is true for heating from a heat pump is at start up. Once it starts running the cost gets lower. The other problem with AC is that it dehumidfies the house and to do this you want the AC to run for awhile not turn on and then off. More insulation can make this a problem. I think we put R45 in our attic. The HVAC guy said don't go any higher than R45 FOR OUR HOUSE due to the equipment he installed.

Later,
Dan

 

[kjsayers]

Thanks for the help.

Another question: What about wraping the hot water pipes in the basement? Worth the $$?

Any other secrets to how i can close up my house besides the weatherstripping of doors and windows and the caulk. Some of the tricks you've heard or done that you just don think of.

 

[heehaw]

the best way to seal a house is by having a blower door test done to locate all the little leaks: next best thing, if you have an attic fan, use the fan to locate air leaks and then seal the heck out of them. if you are building, caulk everything, including where the wiring goes thru the top or bottom plate.
heehaw