How To Insulate a Shed: Complete Guide

Why insulate your shed? Ever gone into your shed in the summer and it feels like 100 degrees? In the winter you have icicles hanging from the rafters after working in it for 5 minutes? I have.

Wouldn’t it be nice to turn that old shed into an extra bedroom or a retreat? How about a man cave or workshop? Those tiny homes sure look good too. I’ve been looking at mine with those same thoughts.

With information, some planning and insulation it is possible to make any shed more comfortable. It’s all open stud construction; all you need to do is to add insulation in the walls and the ceiling. The floor might be more difficult, but even it can be insulated.

I started looking at what is available and what I’d need. You’ve been thinking about it too? Here’s what I found about how to insulate a shed and make it more comfortable.

#1 What to Consider Before Insulating a Shed

Understand the basics of heat transfer

It is important to understand that heat moves from a hot space to a cold space. It is attempting to equalize the temperature in both spaces. So, your shed gets hot from the outside in summer and frigid from the cold in the winter.

•  Conduction: is the movement of heat through solid objects. This is how a shed loses or gains heat through the walls and ceiling. The walls and studs create a continual heat transfer highway in and out.

•  Convection: is the movement of heat through the air or water around you. The heat in your walls and ceiling is moved through your building by air movement. Cracks and openings in your walls and ceiling increase this movement too.

•  Radiation: is the heat waves radiating visibly and invisibly from one object to another. The sun through a window, a fire across the room, sitting on a rock warmed by the sun which then warms you are examples of heat radiation. Sit on a cold chair and your body warms it up. It will stay warm after you get out of it until it has equalized with the temperature of the air around it.

Where you live – Your Climate Requirements

The differences between the inside and outside temperature are key factors. The temperature spread between freezing and the normal household temperature is usually greater than the outside summer temperature and comfortable temperature inside.

If you live in a very cold or a very hot climate you will want more insulation in your walls and ceiling.

Plan How You Will Heat or Cool a Building

It’s important to plan how you’ll heat and or cool your building. It’s much easier to run wires, pipes and ductwork before the insulation is in and the walls closed up.

New installation or existing

Your building may already have some form of insulation in it. You can leave it and add another layer, or remove it and start fresh. If you add more insulation, it usually adds that R-value to the existing insulation.

The R-value of some insulation is affected by moisture, age and compression. Rodents and bugs also like to make nests in some insulation too. Depending on what it looks like and ease of access you may choose to leave it or remove it.

 

#2 What is the R Factor of Insulation?

The R-value is a term tossed around in the construction and renovation industry, articles and media. But what does it mean? After a lot of reading, talking to industry professionals, and even a couple of Engineers, I believe I understand it.

• The R-value tells us how good a material is at preventing conductive air flow or heat (thermal) transfer. It is the resistance to heat transfer of a material multiplied by its thickness. The higher the R-value, the better resistance to heat transfer it is.
  For example: if a 1-inch thick piece of material prevents thermal transfer at a rate of 3.5 times better compared to no barrier, then 4 inches of that material would have an R-value of 14 and 6 inches would be R-21. So, a material with R 38 would be 38 times better at preventing heat transfer than let’s say a plywood sheathed stud wall with no insulation.

• Put simply, which is difficult, the R-value is the resistance (R) of a material to heat transfer through conduction and convection. It refers to the thickness of an insulating material and its heat conductivity based on its thickness. It reflects laboratory testing standards, not actual building applications.

• Insulation slows the flow of heat from inside to outside (keeping the inside warmer), or outside to inside (keeping the inside cooler). The thicker the insulation is, the greater the resistance or R-value to heat movement…usually.

• The recommended R-values depend on the climate you live in. You Building Code or local Inspector can tell you the minimum values required for your area. If you are insulating because it is hot outside (Hawaii or summer only use shed) then you don’t require as much as if you live in a cold zone (Alaska and the northern States or most of Canada).

If it’s hot outside, then R38 to R49 in the Attic and R13 in walls and floors is a guide. If it’s frigid outside, then R50 or higher in the attic and R13 to R30 (or higher) in the walls is a guide. Remember, the higher the R-value, the better the resistance to heat gain or loss.

 

#3 Different Types of Insulation

Form

• Loose-fill / blown-in
  It is composed of particles of cellulose, fiberglass, or stone wool. Usually blown or dumped into finished wall cavities, attic floors, or difficult to reach places. Tends to settle over time so can create cold spots in vertical applications. The R-value tends to increase with compression. Wear a mask and eye protection when using.

• Batts and rolls/blanket
  Rectangles or rolls made from fiberglass, stone wool, plastic or natural fibers to fit between the standard stud and joist spacing. Batts and rolls are great for unfinished walls, floors and ceilings. The R-value tends to decrease if compressed. Wear a mask and eye protection when using.

• Foam or rigid board
  Pre-formed from polymers (polystyrene, polyisocyanurate, polyurethane) they have a better insulating value per thickness than most other materials. They are great for unfinished inside and outside walls, ceilings, and floors. The R-value increases with thickness.

• Reflective
  It is made from a variety of materials with at least one reflective foil surface. It is great for unfinished construction. The reflective surface helps to prevent heat (thermal) transfer and is effective for reducing downward heat loss. The R-value varies with application.

Materials

Fiberglass

Most commonly used and probably the cheapest insulation material. A loosely spun plastic material reinforced with tiny fibers of glass. Some manufacturers are using between 30% and 70% recycled material. Batts are made to fit between 2×4 or 2×6 studs at 16 or 24 inch centers. R-value reduces if wet or compressed.

No products found. R-Value:

• Fiberglass (batts): R-value is 2.9 – 3.8 per inch of thickness
• Loose-Fill Fiberglass: R-value is 2.2 – 4.3 per inch of thickness

Where to use:

• Unfinished walls
• Floors and ceilings

Cost:

• Batts and Blankets $0.64 – $1.19 per sq. ft.
• Loose-Fill Fiberglass 30 cents per cubic foot.

Pros	Cons
Inexpensive and easy to use Environmentally friendly Not flammable Doesn’t shrink	Contains phenol formaldehyde which is linked to cancer Can irritate the eyes and skin; wear gloves, mask and safety glasses. Requires a vapor barrier Can settle reducing R-value

To check the price of the 2×4 Walls Insulation on Amazon, No products found.

Mineral Wool

It is similar to fiberglass but made of basaltic rock or slag from blast furnaces. It also contains recycled materials. It is fire resistant and even holds its R-value when wet. Batts are made to fit between 2×4 or 2×6 studs at 16 or 24 inch centers.

R-Value:

• Mineral Wool batts: R-value is 2.8 – 4.2 per inch of thickness
• Mineral Wool lose: R-value is 2.8 – 4.0 per inch of thickness

Where to use:

• Unfinished walls
• Floors and ceilings

Cost:

• Batts and Blankets   $0.51 – $1.80 per sq. ft.
• Loose-Fill Fiberglass 40 cents per cubic foot.

Pros	Cons
Not Combustible More rigid than fiberglass Easy to cut accurately Good sound barrier Moisture, mold and mildew resistant	Can irritate the eyes and skin; wear gloves, mask and safety glasses. May cause lung disease or cancer if inhaled. Slightly more expensive and maybe a special order.

To check the current price of the Mineral Wool Thermal Acoustic Soundproofing Isolation on Amazon, click here

Cellulose

It is a recycled paper product which is sprayed into existing or new wall cavities or attic floors and doesn’t need a moisture barrier. Its density reduces air flow and heat transfer.

Borate or ammonium sulfate is added to decrease flammability and kill insects. It is not supposed to settle and create cold spots in walls.

R-Value:

• Loose cellulose R-value: 3.1 to 3.8 per inch of thickness

Where to use:

• Blown into Attics
• Blown into wall cavities

Cost:

• Loose-Fill Fiberglass $0.62 – $1.46 per cubic foot.

Pros	Cons
Very compact so a good fire barrier Fire resistant Environmentally friendly; made of recycled newspaper Can be blown into existing finished walls	Allergies to cellulose dust Inhalation of fibers can release boric acid which is a carcinogen Usually require a skilled installer Can be very messy

To check the price of the Cellulose Blow-in Insulation on Amazon, click here

Polyurethane Foam

It is a lightweight spray foam created when two chemicals, polyol resin and a petroleum isocyanate, blend and react. They expand between 30 and 60 times their initial volume.

The spray foam insulation is great for concrete and frame walls, and for hard to reach or odd shaped areas too. It is also available in a board format as a PU-rigid foam (Polyisocyanurate Board or ISO Board), which can be used as an exterior or interior insulation.

R-Value:

• Polyurethane Foam: 3.6 – 8.0 per inch of thickness
• Polyurethane Board: 5.5 – 6.5 per inch of thickness

Where to use:

• Spray on walls and ceilings
• Spray around window and door openings
• Great for crawl spaces and floors
• The Board can be used on exterior walls or on top of ceiling rafters reducing the stud/rafter thermal bridge

Cost:

• Polyurethane Foam    $2.05 – $3.20 per sq. ft.
• Polyurethane Board $0.36 – $0.75 per sq. ft.

Pros	Cons
Highest insulating factor per inch Doesn’t require a vapor barrier Insulates around outlets, wires and pipes Uses less wall space than batts	Not ideal for shed insulation DIY Ecologically unfriendly High cost of installation Toxic until fully cured (approx. 30 days) May cause eye, skin and respiratory irritation or problems

To check the current price of the Closed Cell Spray Foam Insulation Kit on Amazon, click here

Polystyrene – Foam Board Insulation

A thermoplastic foam which is waterproof and also a good heat and sound proof barrier. It comes as EPS (expanded) and XEPS (extruded). The XEPS (XPS) is also known as Styrofoam. EPS is made of beads expanded in a mold, and XPS (or XEPS) is a process that creates a closed cell through continuous extrusion.

R-Value:

• EPS Board (beadboard): 3.2 – 4.4 per inch of thickness
• XEPS (XPS) Board (blueboard): 3.8 – 5.5 per inch of thickness

Where to Use:

• Foundations – interior and exterior
• Under concrete floors
• Walls and ceilings
• Roofs

Cost:

• EPS Board (beadboard)   $0.85 – $1.15 per sq. ft.
• XEPS (XPS) Board (blueboard)   $0.98 – $1.91 per sq. ft.

Pros	Cons
Better R-value per inch than loose fill Can be cut with a hot knife or a saw Some are water resistant Resists termites Recyclable ICF foundations Lightweight	Difficult to fit tightly in stud walls Exposure to sunlight causes deterioration Air spaces in EPS can store moisture, reducing the thermal barrier Not very flexible Environmentally unfriendly

Radiant Barriers and Reflective Insulation Systems

Radiant and reflective barriers are usually installed in attics, as barrier wraps on exterior walls, or as curtains for windows. It has a reflective layer of aluminum foil or reflective plastic.

Instead of just slowing the movement of heat like other insulations, it reflects the thermal energy coming from the sun through the roof or walls back out of the house, keeping the house cool. They are more effective in hot climates or in the summer to keep homes cool.

It comes in a variety of formats, both double sided and single sided; pre-applied to foam boards, batt insulation, plastic or cardboard panels, rolls of plastic sheet, and as bubble sheet. Rigid foam panels with a reflective surface absorb some of the heat but also reflect it. They are applied to exterior walls and don’t require a vapor barrier.

R-Value:

• Polyisocyanurate foil faced: 5.6 – 8.0 per inch of thickness
• Radiant and reflective barriers reflect heat, so have no R-Value
• When combined with insulation, can significantly improve R-Values

Where to use:

• Attic
• Exterior walls
• Curtains

Cost:

• Radiant and reflective barriers $0.13 – $0.47 per square foot
• Reflective Insulation $1.73 – $3.13 per square foot

Pros	Cons
Easily added to the attic Reduces summer heat gain Air and vapor barrier Prevent water and vapor movement	Not effective at reducing conduction or convection Keep away from soffits, vents and surfaces that get hot

To check the price of the Reflectix ST16025 Staple Tab Insulation on Amazon, click here

#4 Checking Air Tightness

 Air Tightness refers to the uncontrolled movement of air from outside coming into the shed through cracks and openings, and air moving out of the shed the same way. The movement of air brings in cold air in the winter and hot air in the summer. It affects air quality and the moisture content in the shed.

Most sheds have air leaks; some are really visible. And of course, they were deliberately left to allow gasoline and chemical smell to escape. However, now that we’re thinking about other uses for that shed it’s time to make it more airtight.

On a sunny day go into the shed, cover all the windows, and note where the light comes in. These are the obvious locations to seal.

The more airtight I can make my shed, the more comfortable it will be in winter and summer; and less expensive to heat or cool. Some of the cracks and openings I’ll close up before to insulating, others will be closed up with insulation.

Indoor air quality, however, requires fresh air, so I’ll have to consider the ventilation requirements too.

Having an energy audit done when you can see the light through cracks and gable ends isn’t logical and costs money that can be used fixing up the shed.

 

#5 Moisture Control

Moisture Control is the plan you develop to prevent moisture from damaging your shed. It will improve air quality and save on heating and cooling costs.

It will also help reduce the growth of mold. It is important to consider the climate you live in too; some are moister than others.

Outside air is the usual cause of moisture in a structure, but poor ventilation will also prevent moisture from escaping. Warm air holds more moisture than cold air, so as it cools it causes condensation on cooler surfaces.

Improper moisture control can lead to wet insulation, framing, and wall board, which can lead to mold growth and wood rot.

All untreated wood needs to be kept dry to prevent moisture from entering the shed. Diffusion from wet wood contributes to moisture in the shed. It is slower than air movement, but the water moves inward to dryer materials through capillary action.

Check that the roof over-hangs and edges are properly sealed from moisture too. You don’t want rain or melt water backing up under the shingles.

It is also important to keep ground moisture from rain and snow melt away from your shed too. Slope the ground away from foundations and use eavestroughs and downspouts to move runoff away.

The aim is to prevent moisture from entering your shed and having proper ventilation to keep everything inside dry. It is an envelope that protects the foundation, walls, and roof from moisture. Otherwise, the inside may look dry, but the insulation is wet and wood structure rotting and moldy.

 

#6 Vapor Barriers

Vapor barriers are great for preventing the diffusion (movement) of moisture through the walls into the wall board and the interior of the shed. But, it doesn’t prevent moisture from air leaks or capillary action bringing moisture into the wall structure and the insulation. It is one part of your Moisture Control plan.

A common vapor barrier, or more correctly – Vapor Diffusion Retarder, is 6 mil poly which has a permeability rating of 0.1 or less (Class I). It is stapled to the stud walls and ceilings after the insulation is installed and before the wallboard or drywall is installed.
Overlap all seams by a foot and tape all seams and cuts. 20 mil poly is great for crawl spaces as it resists tears and punctures and is less permeable to moisture.

If a material has a permeability rating between 0.1 and 1.0 (Class II), it is semi-permeable. Plywood, EPS or XEPS (XPS) polystyrene panels, and 30 pound tar paper are examples of semi-permeable materials.

Materials with a permeability rating of more than 1.0 to 10 (Class III), permit moisture to pass through more easily. House wrap, 15 pound tar-paper, clay and concrete bricks or blocks, untreated lumber, drywall and insulation are all Class III.

It is important to remember that all parts of the shed need vapor barriers in your moisture control plan.
To check the current price of the TRM Manufacturing 610B Plastic Sheeting, 6 Mil, 10′ x 100′ on Amazon, click here

 

#7 What You Need to Do Before Installing Shed Insulation?

 Check if any permits are required.

• Electrical
  Plan out your electrical needs to determine the number of circuits and size of service required. Identify where you want the electrical panel, receptacles, switches and lights. The hot water tank, ventilation system, water pump, and appliances also affect the location of receptacles. Run all wire, and mount receptacle and light boxes before the insulation is installed.

• Plumbing
  If planning for a toilet, you’ll need a septic hook-up and a permit. A sink can drain into a dry-well or grey water tank. Drinking water may come from an existing source or a refillable tank. Consider these decisions in the planning stage. Keep in mind a hot water tank will also need electricity. It is easier to install plumbing, drains and vent pipes into unfinished walls.

• Ventilation
  A proper ventilation system improves air quality and helps to control moisture within a structure. Most unfinished sheds rely on gable vents and the crack and gap airflow replacement method. If sealing the walls and making the shed airtight is the plan, then build in a proper ventilation system; especially if the shed will be for living or sleeping. Running ducts for air exchange is easier if the walls are open.

• Air Channels
  Air channels are the ducts which allow regulated air movement within a structure. The channels shouldn’t be in exterior walls or uninsulated spaces since outside heat and cold can heat or cool the air moving in them, and create condensation and mold growth.

 

#8 How to Insulate a Shed Floor

Insulating the shed floor will help create a thermal barrier between the inside and outside air spaces. Access to the underside of the floor though affects the options available for insulating it.

I have a friend who lifted his unfinished shed to permit the floor to be insulated, then lowered it back down. Budget, ability and experience also influence possible choices.

Most shed floors are open joist construction with a plywood floor. Floor joists usually range from 2”x4” to 2”x 10”; although I’ve seen 2”x3” and 2”x12”. The plan is to fill the space between the joists with insulation to create the thermal barrier.

Remember, the exposed ground facing edge of the joist acts as a thermal bridge for heat transfer into the insulated living space. The only way to prevent or reduce this is to insulate across the joists too.

Retrofit Options

The dimensions of the floor joist influence your options, as does the spacing between joists. If it is 2”x4” or 2’X6” then standard batts can be used. Ensure the batt fills the space but isn’t compressed too much.

You do not want the batt to sag as that creates an air gap between the floor and the insulation and reduces the R-Value to 0.  Mineral wool is more rigid than fiberglass and will sag less.

Cover across the joists with polystyrene with a reflective surface facing up toward the floor. Nail it to the joists with 2” wide head roofing nails and use adhesive glue. Going across the joists creates a thermal break in the thermal bridge.

If the joists are 2”x8” or 2”x10” (or larger), then cut rigid polystyrene into stripe to fit tight between the joists. Use adhesive to keep it in place, and then repeat the steps as with 2”x4” or 2”x6” joists.

Spray foam is a more expensive option and sticks to the joists and underside of the floor and prevents air leaks. If the joists are completely sprayed, then the thermal bridge is broken.

If you’re planning to hire someone to insulate the floor, this is the better one to pay for. The material is more expensive, but the time is less, so it almost evens out.

Another option is to lay rigid insulation down on top of the floor and covering it plywood or OSB. Ensuring the seams of the new floor don’t line up with the seams in the old floor.

Make sure you have space under the doors to permit clearance. This option can be done by itself, or in addition to insulating the joists underneath.

New Construction

New construction is easier to insulate and involves less crawling around under the shed, but follows a similar process. Ensure the spaces between the joists are insulated and the thermal bridge is broken.

 

#9 How to Insulate Shed Walls

There’s a lot to consider when insulating shed walls. How to make them airtight, moisture control, vapor barrier, wiring and plumbing, and whether to insulate inside or outside or both? Much of the process is similar whether a retrofit or new construction.

Cracks and crevices in the walls should be eliminated as much as possible using caulking or another barrier material. A layer of spray foam on the inside of the 2”x4” or 2”x6” walls and gable ends will make them air tight and, once cured, creates a vapor barrier.

An inch of spray foam at R6 would provide R18 at 3 inches thick. The spray foam also seals and insulates around wires, electrical boxes, ducts and pipes.

Using mineral wool or fiberglass batts between studs is less expensive than spray foam, but needs to be cut around wires, electrical boxes, pipes and ducts. Slit the batt to go over wires and pipes, and stuff behind and around electrical boxes.

Batts also require a 6 mil poly vapor barrier to be stapled or tacked to the studs over the insulation. If the walls aren’t air tight, moisture damage can occur inside the walls.

The main difference between retrofit and new construction is the moisture barrier. The moisture barrier protects the whole structure, not just the inside living space.

A new construction moisture barrier would be an ISO board or a polystyrene board applied with or on a reflective barrier, and then a weatherproof siding applied over it. Many shed conversions skip this step.

However, a retrofit would be similar to new construction but applied over the existing wall material. A moisture barrier is a difference between success and comfort, and a job half done.

 

#10 How to Insulate a Shed Roof

How you insulate your roof space depends on how you wish to use the roof space. A gable roof could have an insulated attic or extra usable space.

A cathedral or barn style roof has open rafters which form the ceiling and offer the potential for adding loft space. Each roof style has some different insulating challenges.

A roof is like a hat; it keeps everything under it warm. In areas with a cold climate part of the year, R38 is the minimum and R50 is recommended.

The minimum rating of R38 in a roof requires some creative planning in the roof design of a new shed with 2”x6” minimum roof construction. Even more thinking is needed for a retrofit shed with 2”x4” truss or rafter construction.

Fiberglass with R3.8 per inch would need 10 inches to achieve the minimum requirement. Cellulose and mineral wool would be about the same as fiberglass, and spray foam insulation rated R6 per inch would be about 6.5 inches thick and expensive.

Ventilation is a key part of the heating and cooling of your shed. The insulation resists the transfer (loss) of heat. Ventilation moves the cold or hot air away from the insulated space in the attic preventing moisture build up.

If you fill the existing ventilation space with insulation to get R38, then you’ll need to install a different ventilation system.

In many gable roof structures the soffits are part of the ventilation system. Air enters there and exits at a ridge or gable vent.

Baffles can be installed between the rafters where they sit on the walls to maintain soffit air flow. However, getting R38 at the edge of the wall is unlikely and creates a potential cold spot.

Gable Roof Solution

A gable roof often has a flat ceiling. If you don’t plan to use the attic space for living space, the solution is easier.

Use of baffles to maintain soffit airflow means a potential cold spot, but the main area can be insulated to R38 using batt or cellulose insulation.

Staple or tack the 6-mil poly vapor barrier to the ceiling side if the rafters. Attach your ceiling material so the insulation won’t fall through.

Fill the space between the rafters tight to the baffles, and then lay another layer of batts across the rafters. This will give 10 + inches of insulation and break the thermal bridge.

Cathedral or Barn Style Roof Solution

A cathedral or barn style roof needs proper venting, and insulation shouldn’t touch exposed steel roofing. No solution is easy or without cost.

The best solution I’ve come across was on a cottage Reno 5 years ago. The 20ft. x 30ft. mansard roof with exposed rough cut, or true, 2”x4” lumber with a horizontal stretcher 4ft. from the peak.

The solution involved an Engineer due to the size of the project, but will work for any shed roof; even a gable roof with a livable attic.

To get R38, attach a 2”x6” to the underside of each existing rafter. Predrill the rafters to prevent splitting. Use hangers or a ledger board to support the ends at the walls.

There is now enough space for spay, batt, or rigid insulation to be installed – or a combination. Ventilation is a bit more creative. Remove the shingles or steel, save the steel if in good condition.

Cover the sheathing with 30 pound tar paper or roofing membrane. Attach 2”x2”s at 12” centers to the roof parallel to the rafters. Cover with plywood or OSB, leaving a ridge vent opening.

The open eve ends extend beyond the existing roof and allow air to circulate up through to the ridge vent, providing your roof ventilation. Cover with soffit or screen to keep bugs out.

 

#11 Windows and Doors

Windows and doors are usually the biggest holes in your shed. Most sheds won’t have insulated doors or thermal windows. They are also seldom airtight.

The cracks and crevasses around window and door frames need to be sealed. Use waterproof caulking for small openings and a can of spray foam for larger cracks. If they are big, stuff with fiberglass insulation on the inside and spray foam from the outside.

If you plan to use the storage shed for living space, ensure one window is large enough for a person to exit through; check your local building code.

Consider replacing plywood doors with insulated steel clad doors. You can glue rigid insulation to the plywood doors too. Make sure you have good weather-stripping to seal the doors and windows too.

Consider a storm window that fit over your existing window to provide an extra barrier. They are usually less expensive than replacing the window.

If you want to insulate your metal shed check out my recent article for more details.

Conclusion

I hope you found the article informative. It’s a lot of information to consider. The more planning and preparation you do before you start, the more airtight your shed will be. Having a quiet retreat or an extra bedroom for the in-laws can be a lot of encouragement too.

Your comments are appreciated. If you know someone who is thinking about insulating a shed, share with them if you liked it.