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How To Insulate A Flat Roof From The Inside

Other Forms Of Insulation

Insulation of a pitched roof from inside

Other forms of insulation is by adding a green roof or a living roof on your flat roof. This is basically a garden on top of your flat roof. By putting some type of vegetation on your roof, this greatly reduces heat from being absorbed. And with plants, this also serves as an additional shade for the roof. Just make sure that the integrity of your flat roof is sturdy as the weight of a loam soil is heavy.

Without The Right Insulation Your Flat Roof Is Burning Money Every Month Just Look At The Thermal Images Above

Crazy as it sounds, most older flat roofs in the UK have little or no insulation. So every time the heating goes on, heat and money disappear through the rooftop!

If your flat roof is in that state, the good news iswe can put it right.

It will take some work, though. Its not as simple as showing up with rolls of insulation and laying them in the roof. We need to look at the spec first, and take some remedial steps.

So what type of roof are we looking at?

The Guide On How To Insulate Under Metal Roof Panels

Talking about metal roof insulation, this thing is one of the most challenging things people work in this field is facing. It demands and requires excellent skill and expertise which you may only get from a reputable roofing contractor.

In this article, we are going to explore both financial and technical aspects when it comes to looking for the best method to insulate the metal roofing.

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The Warm Roof Is A Better Shed Roof Insulation Solution Than The Cold Roof

As you can see in the picture below, the shed roof insulation is located above the roof deck.

Section through a ‘Warm Roof’ showing the principal elements

This has a major advantage as both the roof deck and joists are located on the warm side of the insulation. They are both therefore warm and so not prone to water from the warm moist air condensing on them. Hooray!

In many situations this would be the optimum situation and in an ideal world this would be the preferred solution.

Air And Moisture Control


There are five options for installing an air barrier system in an unfinished attic:

  • install polyethylene over top of the joists
  • install polyethylene between the joists
  • spray foam between the joists
  • spray foam under the roof to create a conditioned attic

The first option is the most practical, since installing a polyethylene air and vapour barrier in an existing attic is fraught with obstructions and requires painstaking attention to detail. On the other hand, spray foam offers air sealing and an initial layer of high quality insulation that can be topped up to the desired RSI level.

If the attic retrofit is being completed in conjunction with interior renovations, the easiest approach is to install a new, single air and vapour barrier on the underside of the ceiling joists.

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Why You Need To Ventilate And Insulate Your Flat Roof

Flat roofs on residential homes provide certain benefits, such as easier maintenance and lower installation costs. However, its important to make sure they have proper ventilation and insulation, especially in the Central Florida area due to heat and humidity.

Why ventilate a flat roof? Roof ventilation helps improve air circulation, which offers important advantages for homeowners. Flat roof insulation combined with proper ventilation can help protect this part of your home from moisture damage while also providing other benefits.

A Guide To Properly Insulating Attics And Roofs

Originally published by: JLC OnlineJune 1, 2018by Peter Yost

The following article was produced and published by the source linked to above, who is solely responsible for its content. SBC Magazine is publishing this story to raise awareness of information publicly available online and does not verify the accuracy of the authors claims. As a consequence, SBC cannot vouch for the validity of any facts, claims or opinions made in the article.

The performance of attics and roofs covers a big subject area, so this is the first of two articles addressing this topic. In this first article, we get every one on the same page, explaining the science and options available to builders and remodelers. In Part 2, we will look at the even thornier issues of the evolving building code, real-world roof performance, and some exciting new research in residential roof performance.

Vented, unfinished attics usually work great as built-in moisture buffers. By the word buffer, we mean the space that allows indoor moisture to be whisked away on air currents or to condense on the underside of the roof sheathing where it harmlessly evaporates away or is absorbed into the sheathing and framing before it eventually dissipates . The unfinished attic makes it easy to inspect your roof from the interior.

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What Are The Disadvantages Of External Insulation

  • the price of the insulation material used for sarking is more expensive than traditional materials, but this difference can be compensated for by ease of installation. On second thought
  • the work can only be carried out in dry weather and, in any case, never when it freezes, in order to protect the workers safety,
  • rigid insulating panels are less efficient in terms of sound insulation than glass wool or rock wool materials,
  • you need to hire an experienced company. Achieving an air seal and removing the thermal bridge at the bottom of the slope, in particular, is complicated. Ask for references from the companies from which you are requesting a quote and consult the CSECs advice to fully understand the proposals you will receive.

Learn more about roof insulation

Insulating A Roof: All You Need To Know

The Simplest Way to Insulate a Flat Roof

ByTim Pullenpublished 27 May 20

Insulating a roof is one of the best energy saving home improvements you can make, says Tim Pullen

When it comes to insulating a roof, your choices will depend on:

  • your roof type
  • its structure
  • your willingness to invest

In most cases, extra investment made in beating the Building Regulations on insulation is money well spent it gives a lot back in returns.

Insulating a roof is perhaps the easiest of all the energy-saving home improvements. Mineral wool rolls are ubiquitous and cheap, meaning a whole roof on a standard home could be insulated to the recommended 270mm with a spend of little more than £200.

Its also within the capability of most DIYers, although not the most pleasant of tasks. And the effect it will have on your energy bills depends on what youre replacing and how big your roof is. Its also much more important to do if you dont have any loft insulation at all.

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Choose The Insulation Material

There are a lot of options available in the case of insulation materials such as polyisocyanurate, expanded polystyrene, extruded polystyrene, and many more.

The most popular among them is polyisocyanurate with a higher R-value and is mainly used in the existing flat roof insulation process. Extruded polystyrene is comparatively cheap and also gives a good performance.

After choosing a material that fits well with your requirements, you can proceed further.

Insulating A Flat Roof

I am currently a licensed contractor performing remodeling services for residential and commercial customers in Wisconsin.

Read my step-by-step guide for flat roof insulation.

Flat roofs have been a daunting task for contractors and homeowners alike since they were invented. They are hard to waterproof, hard to maintain, and hard to insulate. For today’s purposes, we will stick with the insulation issue.

In order to properly insulate a flat roof area, you need to be very careful on the material and the methods used. I will break these into sections for organizational purposes:

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Blog Post: The Ten Golden Rules For Foam

In this blog post we summarize the knowledge gained from the above two documents – and other sources – while making it relevant to US cold climate construction. The Golden Rules include: 3% minimum pitch, dark membrane, no shading, check wood moisture content, use intelligent vapor retarder, do not install humid insulation, no cavities in insulation, verified air tightness, do not vent, breaking rules is possible but must WUFI. Read the blog post here.

General Considerations For All Attics

Building and insulating the flat roof

Figure 5-1 Types of attics

Regardless of the type of attic or ceiling your house has, there are a number of things to examine before beginning work. A thorough inspection of the following features will help you to develop your retrofit strategy.


Most houses with accessible attics have an interior ceiling hatch, although exterior roof or wall-mounted entries are not uncommon. A hatch should be large enough to allow you to bring in materials. If not, or if there is no access, you may be able to cut a hole in the ceiling in an inconspicuous place such as a closet. Exterior-mounted, gable-end entries represent one less opening that will have to be air sealed, which offers ready access to firefighters in the event of a fire.

Check the roof space for obstructions and ease of movement. Vertical clearances of less than 1 m will not allow you to move freely. Attics or roofs without a working space are covered later in this chapter, in Part 5.4, Cramped attics, cathedral ceilings and flat roofs.


Moisture can come from the outside due to failure of the roof or flashing. Typical problem areas include poor flashing at a hip, valley or the chimney and ice dam leaks. Pay particular attention to water marks on the underside of the sheathing or along rafters.

Figure 5-2 Some attics are easier to work in than others

Existing air and vapour barriers

Figure 5-3 Keep combustibles away from a masonry chimney

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How Much Insulation Is Needed

How much insulation is enough to protect your home is always a burning question.

Sometimes people make the mistake of thinking that if they insulate the attic more, then their home will be properly insulated, but that is not the case. Initially, this seems to work but in the long term, this does not make much of a difference.

Scientifically, the isolation amount is directly related to the U value that depicts the temperature difference in your house.

Why Its Important To Insulate Your Flat Roof

While insulation for a flat roof is expensive and can account for as much as 25% of the total installation cost, there are a number of important benefits to having it in place.

1. Reduce extreme temperature fluctuations inside your home

When you have an un-insulated roof, you have to live with rather uncomfortable room temperatures inside the home. During the cold months, warm air will quickly rise up and escape through the roof, leaving the rooms very chilly.

The opposite happens in the summer: hot air gets trapped inside, making the room unbearably hot and sticky This is particularly true on roofs that are dark and have a low insulation r value.

It is important to note that Polyiso has the best performance in warm climates. Its insulating properties are worse in extremely cold temperatures. If you live in a region that is cold for many months of the year, you should consult a professional on the best insulation type for your house.

2. Improve energy efficiency

A roof without good insulation is a great contributor to energy loss. This is bad for the environment and for your wallet, as you end up spending a lot more on your electric bills.

Proper insulation can significantly reduce your energy consumption and reduce your energy costs by hundreds of dollars a year.

A high r value of 20 or more, combined with well insulated walls and energy efficient windows can reduce your heating and cooling expenses by as much 30% every year.

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Air And Vapour Control

Where you have access to the attic space, follow the directions for the control of air and vapour flows as outlined in Part 5.2, Easily accessible attics.

Houses with half storeys have one major source of air leakage that must not be overlooked: through the ceiling joists immediately beneath the knee walls . This critical air leakage area must be sealed flush with the back of the knee wall finish. This can be done by cutting and fitting foam board that will fill that ceiling joist opening and seal it into place with caulking or spray foam.

Another option may be to dense-pack loose-fill insulation between the floorboards and the ceiling below while ensuring that an air barrier is installed.

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Flat Roof Insulation What Does It Depend On

Dormer roof insulation (warm deck)

The basic decision to make when it comes to thermal insulation of a flat roof is the material. The one you finally choose depends on several factors, such as the arrangement of the layers of particular materials, the way the roof slope is used, and the type of roof. Remember that this process is different for insulating a non-ventilated roof and different for a ventilated roof.

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How Long Does Flat Roof Insulation Last

Insulation materials tend to be extremely robust. You can expect flat roof insulation to last anywhere between 25 and 40 years. Its worth noting that warm roof insulation tends to degrade faster than cold roof insulation due to it being exposed to the elements. However, this shouldnt cause too much concern as the insulation will last at least as long as the durable waterproofing material.

What Is A Warm Roof Deck And A Cold Roof Deck

A warm roof deck is the most common and most preferred type of flat roof build up in the UK. A flat roof where the insulation sits below the waterproof membrane and above the structural deck is a warm roof deck. Cold flat roofs are typically avoided as youd need to install ventilation, which can prove problematic for many reasons relating to space, labour costs, etc. Warm flat roofs do not need to be ventilated as the insulation is above the structure.

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Five Ways To Insulate An Unvented Low

Of the various methods to insulate a shallow roof, applying insulation to the exterior is easier than working in a space with limited access. Whatever method is used, the amounts of insulation must achieve R-values mandated by local codes.

1. Exterior rigid foam

Install a thick layer of rigid-foam insulation above the roof sheathing.

Why Do We Need Flat Roof Insulation

Building and insulating the flat roof

As heat rises, most energy loss is usually through the roofing area. Flat roof insulation is an essential tool that can enhance the energy efficiency of a building and reduce fuel costs.

Creating more effective flat roof barriers also offers your building further protection from the unpredictable outdoor climate, including overheating in warmer climates and rain and snow in cooler regions.

From high rise apartment blocks, to residential designs, industrial units, large commercial facilities and schools or hospitals, flat roofs are an integral part of modern building design.

Constructions such as terraces, rooftop gardens, blue roofing with water retention and roof spaces which are used for solar purposes are becoming ever more popular. This growing trend for functional roof spaces brings even more demand for effective insulation, helping to enrich the space available on top of your building.

Relevant resources

Kim Brandt

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Bonus Rule: Want To Break A Rule Have A Professional Wufi It

You can follow all the rules above, and even break a few, with a professional WUFI analysis.

Current building code for unvented roofs is written for the mainstream, spray foam industry and therefore specifies air-impermeable insulation, or foam. This is due to a lag in educating code officials on alternative safe and robust systems, as we noted in our blog post, Yes, Unvented Roof Assemblies Can Be Insulated With Fiberglass. However, the intent of the code can be readily met with an assembly that includes fibrous insulation and an inboard air barrier and vapour control layerand is approved for use as such.

If you are in a cold climate and are considering one of our suggested assemblies, review it with your local building department official. Have a certified professional perform a WUFI analysis of the assembly or alternatively, have an architect or engineer approve the drawings. In most cases, weâve found that a foam-free solution is possible.

For Energy Efficiency Reasons

  • the thickness of insulation can be at the maximum, not limited by the thickness available between the rafters as is the case in the interior technique.
  • the existing roof trusses and purlins are now entirely included in the protected volume and therefore protected from strong variations in temperature and humidity.
  • thermal bridges at the rafters are non-existent, contrary to the case of insulation from the inside.

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Fire And Other Hazards In Attics

Metal chimneys

Factory-built metal chimneys should be kept from contacting insulation by a minimum 75 mm unless otherwise specified by manufacturer or local authorities. Install a non-flammable radiation shield that maintains a 75-mm air space between the chimney and insulation. To reduce air leakage, first air seal the fire stop to the air and vapour barrier with non-combustible sealant. The top of the radiation shield should also be a minimum of 75 mm higher than the level of existing or new insulation to be added. To prevent insulation from falling behind the shield, attach a clamp-type storm collar without sealant at the top of the radiation shield.

Figure 5-5 Keep insulation away from a recessed light fixture by creating a barrier

Minimum 12.5-mm clearance, 150 mm preferred

Centre the fixture if possible, keep it a minimum of 12.5 mm from the sides and top

12.5 mm plywood box lined with a fire-resistant material such as drywall or sheet metal to provide airspace around the fixture caulk all joints and edges of the box to minimize air leakage

Minimum box volume â allow 800 cubic centimetres per watt of the fixture

Electrical installations

Work safely around electrical wiring . Consult with an electrical contractor if questionable wiring or corroded electrical connections are present.

Recessed lighting

Animal droppings

Seal the following areas:


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