DIY Attic Insulation: How to Insulate an Attic

September 9, 2014
niki dube

Is Your Old DC Attic Leaking Air (and Money)? We’ll Show You How to Fix It

This post is part of our Max DYI Series, which provides you with the tools, tips and tricks you need to tackle your own home insulation projects.

As a household DIY project, insulating your attic is a good place to start if the goal is to prevent losing up to 30% of your climate controlled air. A properly insulated attic will provide immediate comfort during summer and winter seasons and a fairly quick return on your household improvement investment.

However, keep in mind, it is only part of the overall solution to insulating your home. By including air sealing and radiant barriers, you have the potential to reduce your home energy by an additional 20%.

Like this post? Check out the rest of the Max DIY Series

All attics are not the same. DC homes have a range of architectural styles and attic types from Wardman, Federal, Cape Cod, Craftsman, Georgian to Colonial and also Sears Catalog bungalows. The DIY project plan below tries to capture the many different types of attics with each of these styles.

Let’s begin your attic insulation project with blown insulation.

Attic insulationThe diagram shows a typical attic and how air circulates from the soffit vents up and out through the ridge vent. With blown insulation, you do not want to disrupt the circulation of you will introduce moisture into your attic and a host of new problems. Reflective insulation is radiant barrier (see MAX DIY Blog #5).

Getting started: In the worst of conditions, prepare to get dirty, fend off spiders, sweat in summer and freeze in winter. In rare occasions, especially old homes where gaps allow in inspects you might come across wasps nests. Dress appropriately and have a positive attitude.

For an average size DC attic of no more than 1,000 square feet in a DC Wardman row house Federal or Cottage/Cape Cod style home, this should be a half-day project, plus another couple hours purchasing materials from your local hardware store and securing a rental blow machine early enough in the morning before someone else gets it. Moreover, add another few hours if you have to go to Home Depot and find someone who knows something, and if you need to install recessed light covers and baffles.

Attic accessibility will also determine the timeframe for this project. Many of the Wardman and Federal style row houses have flat roofs without direct access to the attic. This will require cutting holds in the ceiling sheetrock to access the attic area, and then replacing the sheetrock, by mudding, taping, sanding and painting. It’s called mudding for a reason. For simplicity, let’s assume you have easy access to the attic.

What’s You’ll Need

Tools and Materials
  • Air filter mask. (Attics are generally dusty and if old insulation contains asbestos or formaldehyde, a good air filter mask is a must.)
  • Work gloves. (Make sure they are snug, form fitting gloves. While balancing on the rafters you’ll want to quickly find a good grip overhead to avoid falling through the sheetrock into the living room below.)
  • Light. (If there is no attic lighting, use a bright work light or headlamp to free your hands when walking and balancing on the ceiling joists. This is not a job for working in the dark.)
  • Knee pads. (recommended)
  • Tape measure.
  • Chalk.
  • Recessed Light Covers. (Non IC rated recessed ceiling lights require in-attic covers. Covering a hot ceiling lap or bathroom fan with insulation can be hazardous.)
  • Baffles or attic vents. (If your home has vented soffits, you will need baffles to prevent moisture, mildew and fungus growth.)
  • Staple gun. (For the baffles, if required.)
  • Insulation blow machine with minimum 3 inch diameter pipe.
  • Long extension cord. (You may need two depending on the machine requirements plus another for attic lighting).
  • Loose fill Insulation (choices are cellulose, rock/slag or fiberglass).
  • Optional: insulation removal machine and construction quality garbage bags to dispose the old material.

Got all that? Okay, let’s get started.

Amount of Insulation

For a DC attic, the Department of Energy recommends achieving R49-R60 protection. With standard fiberglass (2.22 R Value/Inche) or cellulose (3.21 R Value/Inch) insulation, the thickness should reach from between 15 to 27 inches, less what is already in place. To determine number of bags of insulation based on R-Value and square footage of your attic, go read this post:

Determining Proper Wall Insulation and Attic Insulation Amounts

Armed with the right attitude, tools and materials, the next step is to assess the attic situation.

Assess the Attic

Step1: Evaluate Type of Insulation

What type of insulation is currently in the attic? Many flat-roofed homes in DC are without insulation. In pitched roof attics, insulation will either be batts (rolls) under the roof sheeting, along knee boards or on the attic floor. If you have vermiculite insulation in your home, you should remove it. With vermiculite insulation, assume this material is contaminated with asbestos and have it removed professionally. Go to to learn how to protect yourself and your family from exposure to asbestos.

Step 2: Condition of Insulation

If your home consists of old insulation that may be mildewed or moldy from a leaky roof, remove it. Wet or moldy insulation provides no insulating properties. A leaky roof also needs to be fixed.

Step 3: Current R-Value (Quality and Coverage)

The quality and amount of insulation in the attic will determine its R-Value. R-value is the measure of resistance to heat, which is the overall insulating property. If some quality insulation is already in place and you wish to add more to achieve R-Values of 49 to 60, then add only what is necessary.

Step 4: Survey for Air Leaks

Air leaks allow drafts of cold or warm air to enter or escape your climate-controlled home.   Gaps that allow air leaks should be properly filled. Air leaks are typically from attic stairs, stairwells, ceiling junction boxes, ducts, lights, fans, gaps from old construction. There is little point to insulating the attic if there are gaps that allow air leaks. Air leaks can be filled with loose insulation, batts and spray form. (See the Max Insulation DIY blog #6: Top 10 Gaps and Air Leak Projects).

Step 5: Assess Soffit Airflow and Ventilation

Attics with eves and vent soffits will require baffles. Baffles allow the circulation of air from low to high from the soffit to the upper ridge or roof vents.  Without soffits, it is important to understand how the attic air circulatory system was designed to avoid interference with the blown in insulation. Proper circulation of air through the attic prevents mold and moisture.

Step 6: Consider Radiant Barriers

Most homes in DC do not have radiant barriers. Radiant barriers block out up to 95% of radiant heat, which is directly related to the sun. If in place, evaluate the condition of the barriers and check that proper adhesives are used to attach the radiant strips together to create an airflow barrier. To learn more about radiant barriers, see the Max Insulation DIY Series blog #5 Radiant Barriers, The Overlooked First Line of Defense in Winter and Summer.

Step 7: Evaluate Skylight Insulation

If your home has a skylight, as many DC homes do, it will be important to insulate around the exterior of the inside box with the right materials. There are several approaches you can use: wrap the skylight box with batt insulation, use an insulation blanket, or cut to size and attach foam board insulation. With foam board, make sure you are choosing quality products that are fire resistant and meet code. Skylight boxes do not provide your home protection from attic and outside temperatures.

To learn more, read: Insulating Skylights

Step 8: Prepare the Attic

Attic floors are unforgiving so setup proper lighting. You must step carefully from joist to joist. Consider using 1” by 8” planks to create a path for walking or a spot for kneeling. Be careful. A wrong step with too much weight will punch your foot through the ceiling of the room below you. Also, be mindful of the sharp roof nails protruding through the roof sheathing.

Insulating the Attic

Step 1: Attaching the Baffles

If your home has vented soffits, you will need to attach by staple baffles. The baffles are attached to the roof sheathing (plywood) between the trusses starting at the attic floor. The insulation lays up against the baffles to allow air to circulate from the soffit through the attic to the upper ridge or roof vents.

Step 2: Blown Insulation

With tools, equipment and a safety plan in place, you are ready to insulate your attic.

Following closely the instructions on the blowing machine, spray the loose insulation throughout the attic. Begin in a back corner and be sure to blow in sufficient amounts of insulation in the dark corners above the eves.

Finishing the Project

When you are done, drink a cold beer and congratulate yourself on developing a new skill you are unlikely to ever use again. Nice job!

Oh, and if this seems totally overwhelming (or just boring), don’t worry! That’s what we’re here for.

Contact Max for a free consultation and estimate to live more comfortably in your home for less cost. Call or email us at or (202) 341-6015 (ask for Max).