How to insulate an attic of an old house?

Author: Dr. Jedidiah Ward  |  Last update: Wednesday, February 12, 2025

You can add R-30 insulation batting throughout your attic. Or, you can also use blown-in insulation which has environment-friendly materials available. A 15-inch thickness is like the R-30 insulation batting. For a greener insulation project, Cellulose blown-in insulation is available.

What is the best insulation for an old house attic?

Fibrous Insulation that is blown in works best in most attics. Fibrous can be fiberglass, cellulose or rockwool. You can install a 2 part spray foam, either open or closed cell. You can install a rigid foam insulation. The cost of labor to properly install rigid foam makes it prohibitive.

How do you insulate an already finished attic?

Spray Foam: More often than not, spray foam insulation is the better recommendation for insulating a finished attic. Spray foam expands to fill every nook and cranny, ensuring your attic is well-sealed and insulated.

Where should you not put insulation in the attic?

Also, when laying down additional insulation, work from the perimeter toward the attic opening. Never lay insulation over recessed light fixtures or soffit vents. Keep all insulation at least 3 inches away from recessed "can" lights, unless they are rated IC (Insulated Ceiling).

Is it okay to put plywood over insulation in an attic?

Can I put plywood over insulation in the attic? Yes you can install plywood subflooring directly over the floor joists and insulation on your floor. You need to install rigid insulation boards on top of the attic flooring joists and then install plywood over the top.

How to Beef Up Attic Insulation | This Old House

Can you put too much insulation in an attic?

Too much insulation will leave humidity and moisture to accumulate in your attic space. This can lead to mold growth on your walls and insulation. There might also be water damage to the support beams in your home's roof.

Should you remove old attic insulation before adding new?

Removing old insulation is generally recommended if it's damaged, contaminated with mold, or infested with pests. However, if the insulation is in decent shape and just needs a boost, adding a new layer on top can be a cost-effective option.

What time of year is insulation cheapest?

Best Time of Year to Buy Insulation

In this case, the spring is the best time, because you will also start to see savings in the summer months. The same is true for warmer climates, just different times of year because you'll want the job finished before the heat sets in.

Can I insulate my attic myself?

With certain types of insulation materials, installing your own insulation is definitely doable—and you can save money not hiring a professional. Installing fiberglass or mineral wool insulation are simple DIY projects. Other insulation types, such as spray foam insulation, require the use of a professional.

Do you need 2 layers of insulation in attic?

Overall, the second layer of insulation plays a crucial role in improving insulation performance, reducing heat loss, and maintaining a comfortable and energy-efficient living space.

Does a finished attic need to be vented?

An attic without ventilation loses energy through ceiling fittings and leaky ducts, costing the homeowner as much as 20% in energy cost. When moisture is allowed in an attic that is unvented can lead to roofing issues. Wet roofing panels are subjective to ice dams that damage shingles.

How to insulate a ceiling from inside?

The best way to insulate the inside of a ceiling depends on the type of ceiling and your specific needs. Spray foam insulation and batt insulation are two popular options. Spray Foam Insulation: This method involves spraying a liquid foam that expands and hardens.

Should an attic be sealed or vented?

In hot, humid locations, it may also be advisable to construct unvented rather than vented attics to help reduce the entry of moisture-laden air into the attic. In hot, humid locations, the outside air is likely to be more humid than the inside air.

What is the lifespan of attic insulation?

Conclusion. Attic insulation can last 80 to 100 years, though it loses its energy efficiency benefits with time. Certified attic specialists' professional advice is to upgrade it every 15 years to ensure that it is still performing the job.

Should I insulate my attic floor or ceiling?

Insulating your attic floor can create a vented attic, which is ideal for storage and not needing temperature control upstairs. Insulating the ceiling will make an unvented attic, which allows you to control the temperature for temperamental storage items, living space, and HVAC ductwork.

How much does it cost to add insulation to an attic?

Attic insulation costs anywhere from $1,680 to $3,125, depending on the size of your attic and the material used. On average, most homeowners shell out around $2,380. These costs include the insulation materials and installation by a professional.

Is blown or rolled insulation cheaper?

Rolled insulation generally has a lower upfront cost than blown insulation. However, blown insulation tends to have a higher R-value, meaning it can provide superior attic insulation, creating potential for cost savings on heating and cooling bills in the long term.

Should I replace 20 year old insulation?

However, insulation can start falling from fiberglass batts after 15 to 20 years, so if your insulation was installed in batts well over a decade ago, it might be time for an inspection or a home energy audit.

Can too much attic insulation be bad?

While loft insulation is an effective way to improve energy efficiency and reduce heating costs, over-insulating can lead to several potential issues. Firstly, over-insulation can lead to poor ventilation in the attic, which can cause moisture buildup and increase the risk of mould growth.

What to do before attic insulation?

Before installing insulation, first seal any cracks that allow air to flow from the living area into the attic. This prevents moisture-laden air from reaching the attic where it can condense, leading to mold, wet insulation, and possible damage to building components.

Where should you not put insulation?

Never place insulation close to water heaters, oil burners or anything hot. The backing is especially flammable and will be a major fire hazard for your home.

Can your R-Value be too high?

Now, to answer whether R-Value can be too high, the answer is technically no. The higher the R-Value, the better the insulation will reduce heat transfer. However, a few things to remember when choosing an insulation R-Value.

Is it okay to cover attic insulation with plywood?

Before laying plywood over an insulated attic floor take a look at the existing insulation. If it is batts, make sure the paper side is down. Also make sure the existing insulation isn't extending over the top of the joists. If so you may need to spread it around as compressing it will cause it to lose it's R-Value.

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