Is it best to spray over existing insulation and how much dose it usually cost to do a house built in 1956, about 1800 sq feet?
Can we do it ourselves? Where would you get the machine and product needed for the job?
If its blown in insulation you can spray over the existing insulation. Blown in insulation runs approx. .75 to $1.00 per square foot installed.
You can contact your local equipment rental store or roofing company for insulation blower rentals.
If you've never done it yourself I would suggest calling in a professional.
I have added extra insulation for my personal residence by blowing insulation over top of existing fiberglass.
Blown cellulose is the insulation I would recommend as mice and other rodents do not like it. Most homes with blown fiberglass have an attic that is riddled with rodent holes and excrement throughout the attic. Mice can walk straight up a brick wall so it is almost impossible to keep them out.
Lowe's had a blowing machine that they gave you for FREE if you bought 20 bags of cellulose insulation at around 9 to 10 dollars a bag. Simple to use, except very heavy, and just need gloves and air filter mask.
Good Luck with your project.
Excellent information given already. I agree with cellulose as the preferred insulation. It is similar in cost to blown fibreglass but the borate treatment given cellulose is insect resistant and acts as a fire retardant.
Have a look at this video for a comparison: http://youtu.be/7V2I1tBcBuc
You can do it yourself however it is similar to Insulated Concrete Forms that are sold through the Building Centres. You can do your home foundation yourself as well, but if you do not know how to do it correctly, your house could quite possibly collapse. Likewise, if attic insulation is not done correctly, you can quite easily create a situation that will rapidly rot out your roof rafters (or trusses) and sheathing. The hardest part of the installation is the preparation. Afterwards, the actual blowing in of insulation is actually almost fun (but quite messy and hard on your lungs so wear masks and seal off any penetrations).
The key concern is proper ventilation of your roof framing. You must block off your soffits prior to the commencement of blowing in the cellulose. If the soffits become blocked or clogged with the insulation you no longer have convection air flow under your roof sheathing which can lead to water vapour in the air leaked from your home to condense on the underside of your roof framing and quickly lead to rot. The airflow promotes drying and the evacuation of moist air from the attic space (assuming proper roof or ridge vents for the surface area of your roof).
Once the insulation is done, the blocking must be reduced to permit at least 2 1/2" of air space above the insulation and under the roof framing. This must be done in such a way so as not to compromise the very important area at the top of your exterior walls.
Also prior to blowing in the insulation, take the time to push the existing insulation aside atop interior walls and take the time to inject spray foam (or better, fire caulk) into the penetrations for wiring and plumbing.
I suggest a professional, but either way, best of luck.
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