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How To Insulate A Flat Roof From The Inside

Insulation In Tricky Spaces

The Simplest Way to Insulate a Flat Roof
Dick Clarke explores how to insulate unconventional spaces, from ceilings to slab floors, and make your home even warmer in winter and cooler in summer.

Everybody knows you can install insulation batts on a flat ceiling, and that sarking goes under roof tiles. But how do you insulate the tricky places? What can be done when renovating? And how should insulation be installed to avoid condensation, discussed in Sanctuary 18? Here are some suggestions for insulation that are not always considered.

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.

  • Radiant Barrier Spray Metal Roof Insulation
  • Mistake # : Save Money By Installing Fiberglass Insulation And Framing Out Roof Slope Using Osb Board Substrate

    When a homeowner really needs to cut down on costs, some contractors may suggest the following:

    Add an additional layer of OSB over the sheathing. It should be installed on tapered 2x furring strips, in order to slope the surface of the roof to drains. Then, install R-30 fiberglass batts between the rafters.

    Our Take: Framing this out and buying 30-R fiberglass insulation will cost you about 50% more than just buying 5 inches of PolyISO .

    Because it will take a lot of time to actually install all of this, you are risking major leaks, if it starts to rain before everything is complete. Also, if a roof leaks and fiberglass insulation gets wet, it will loose most of its insulating properties.

    Moreover, you are also risking that underneath this wet insulation, you roof sheathing and deck will start to rot. The worst part about this: you will not even know its happening. These problems typically come out when its too late to fix the roof, and complete replacement is in order.

    However, PolyISO absorbs considerably less water, therefore if it gets wet, it looses only a small fraction of its insulating properties. If moisture is a major concern, you can also install XPS rigid insulation, which offers superior moisture resistance.

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    What Is The Best Way To Insulate An Attic Roof

    Better materials for attic roof insulation are rigid foam boards and spray foam insulation . Spray foam: Technically known as Spray Polyurethane Foam or SPF, spray foam is most commonly applied in the space between attic rafters. It can act as an air and moisture barrier in addition to providing very high R-value.

    Air And Vapour Control

    Loft Insulation

    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

    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.

    Ten Golden Rules For Foam

    When insulating a flat roof wood structure, 475’s goal, as always, is to do it in the most healthy, structurally sound, durable, and ecologically friendly wayachieving truly high performance. This means we try to avoid using foam above or below the roof deck whenever possible

    With foam out of the equation, we examine how to avoid condensation, rot, and mold in our structures. Based on the research noted in our post, Unvented Flat Roofs: A Technical Discussion, we have established The Ten Golden Rules. Follow these rules to ensure a robust roof assembly.

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    Understanding The Cold Roof Method

    The cold roof method has been widely used in the past. However, it is not recommended nowadays, considering that it can cause condensation and may damage the roof structure in the long run.

    Though you can install a ventilation system to prevent such from occurring, the cold roof method is still disadvantageous because of the labor cost and the fact that it reduces the internal space of the house. That is why experts advise using a warm roof deck as an alternative to insulating the roof from the inside.

    Hot Roof System: Recommended By Experts

    How to Insulate a Flat Roof , Floor , Stud Walls & Calculating U Values

    As mentioned earlier, experts do not recommend insulating a flat roof from the inside anymore. Instead, the current trend is to insulate using a hot roof system, otherwise known as a warm flat roof. This type of insulation does not lead to condensation. Instead, the insulation material is put on top of the roof structure.

    A warm roof deck usually uses at least 100mm of rigid insulation placed on top of the roof joists or the vapor control layer. Then, another layer of a waterproofing system is applied above the insulation material. No ventilation is required for a hot roof system.

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    Use A Minimum Roof Pitch Of 2% Or 3%

    Shedding water is always the essential first step in preventing leaks and keeping your roof safe. This is why, in reality, flat roofs are not perfectly flat. Roof pitch, also known as the grade or slope, is a measure of vertical rise to horizontal run, measured in inches per 12 inches

    We recommend that the pitch be a minimum of 2-3% to prevent water from ponding. This provides a buffer for potential deflection, or sagging, of the roof under a load over time. New York architect, Chris Benedict, leads by going even further, using a pitch of 1/2:12 for her flat roofs.

    Ponding water from inadequate pitch.

    How Does A Warm Roof Solution Work

    For a warm roof solution you will need toinstall insulation in the plane of the roof pitch, that is, immediately below the sloping roof. This will help to avoid your roof-space becoming excessively hot in summer or cold in winter, and will reduce heat losses from your roof. Assuming you don’t have a room in the roof, and it is just a ‘loft’, then you should also implement all the ‘cold-roof’ insulation measures described above, including any raised boarding as appropriate.

    One important point to remember with a warm roof solution is the need forventilation immediately below the roof tiles. This is to prevent any condensation build up, or water getting in through or around the tiles. You need to create a space for air to flow parallel to the rafters and immediately under the tiles from one side of the roof to the apex and down to the other side, otherwise the roof structure may begin to rot.

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    Insulating And Venting A Shed Roof

    Tom Jordan is a painting contractor in northern New Jersey whos at his wits end as he tries to figure out a remodeling job at his own home.

    It seems simple enough. Jordan is turning a three-season room on his 1930s house into a fully conditioned space. The room measures 12 feet by 16 feet and has an 8-foot ceiling. The flat roof overhead is framed in full-depth 2x6s, finished with what Jordan believes is roll roofing .

    My issue is how to correctly insulate the ceiling, he writes in a Q& A post. Ive spent what seems like hundreds of hours online and had a few insulation contractors look at the room, and I cant believe the inconsistencies that exist on this subject.

    In Climate Zone 5, the prescriptive table of the International Residential Code requires at least R-49 of ceiling insulation. With 2×6 rafters, thats a tall order, and Jordan adds a couple of major caveats.

    The roof is only four years old, so removing it is not an option, he says, ruling out a layer of exterior rigid foam. The room does not have any venting, nor is it possible to vent Before anyone suggests closed-cell spray foam, Im ruling that out. I have no confidence in the healthiness of the product. It might be a great product, but I dont want it in my house.

    Those are the ground rules for this Q& A Spotlight.

    You need exterior insulation

    You need

    Installing A New Roof

    Insulating Flat Roof From Inside Ceiling

    When re-roofing, remove the roof finish and the sheathing, air seal and fill the cavities with insulation and then install the new roofing materials, including an ice-shield membrane. A well-sealed roof will need little to no ventilation. If you are uncertain about whether or not the sealing can be done effectively, leave a ventilation channel under the sheathing from the soffit to the peak. Sometimes insulation can be added to the ceiling inside, although this approach will not stop the air leakage.

    An alternative measure to prevent ice dams is to make the roof impermeable by using a self-sealing membrane under the shingles. Building codes require such membranes on the lower part of the roof in new houses. These membranes do not stop ice dams, but they prevent the water from leaking through the roof sheathing and into the house. Ice damming can still occur and possibly damage shingles and gutters.

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    Dont Shade The Roof Membrane

    Any shading will prevent the sun from driving the humidity out of the assembly. Meeting this Golden Rule means NO: pavers, terraces, gravel, green roofs, or solar panels. If you have surrounding structures that might shade the roof or pitched solar photovoltaic panels, again a WUFI analysis can determine what’s possible.

    Wood moisture meter

    Prevent Rotting Of The Sheathing And Roof Deck

    Across the US, the majority of flat roofs either have no ventilation at all, or are poorly vented. This is due to faulty original architectural design that did not take proper venting into account.

    As a result, if you open up most flat roofs, especially those located in places like Arizona, you will see a lot of moisture, rot and mold as a result.

    This problem also occurs in roofs that have fiberglass batt insulation and no venting. Sometimes, inspectors find that it is completely wet there is severe rot and mold growing in the sheathing.

    To mitigate venting issues, and still have all the benefits insulation offers, its ideal to install high quality foam board products, such Polyiso or XPS. They are not susceptible to moisture infiltration and will keep the roof dry, even without a good ventilation system.

    You just need to make sure that you put in enough insulation to keep the sheathing above dew point temperature in the cold months. For best protection, professional contractors recommend at least 6 inches of foam insulation board.

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    Flat Roof Insulation Options

    Adding insulation to an existing flat roof is a labor-intensive process. While you can choose any of the common insulation options, some will work better than others, both with your specific building and with your specific roofing system.

    • Polyisocyanurate: This material is the most popular flat roof insulation option. It is closed-cell foam, achieving a high R-value, even for minimal thickness. You may need that thinness if youre working with an existing flat roof with little space.
    • Expanded Polystyrene: While a great option for new flat roofs, this material may not be best for existing flat roofs as it works by expanding into crevices. Care must be taken to avoid cutting off ventilation.
    • Extruded Polystrene: Not as high-performing as the expanded version, but easier to install in existing roofs.

    The cost of taking off the top parts of a flat roof in order to add to the insulation may be costly, especially on larger commercial buildings. However, they are often much less than the cost of repairing and ultimately replacing a cold roof that fails early. Ensure that your new insulation doesnt impact ventilation to protect your investment in your roof and your property.

    So How Do You Insulate A Flat Roof Or Ensure You Have Adequate Insulation Already Installed

    Thermal Bridging of an insulated flat roof through the front fascia

    That is a question asked by a lot of homeowners when it comes to their flat roofs. Inadequate insulation costs money. Not to mention the increase in discomfort both in the winter and the summer. So having a properly insulated flat roof not only saves you money, it increases your comfort levels by maintaining the temperature in the house to a respectable level.

    Most residential flat roofs are constructed of I-Joists or open web 2 x 4 construction topped with OSB underneath the weatherproof layer of roofing material. This leaves very little space for insulation. The contractor can and usually will insulate the space between the joists as best they can but it still is not an effective method, so the basic option is to insulate from the top by adding a layer of rigid foam overtop of the OSB board.

    This method works but the R-Value or efficiency of the insulation is limited due to the restrictions on thickness of the foam.

    Another method commonly used when insulating a flat roof is to layer the roof with tapered deck which gives some space for insulation and adds a slight slope to the roof giving it a more effective way of shedding water.

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    Radiant Barrier Spray Metal Roof Insulation

    A stark reality might be happening in a few decades later when it comes to energy usage. In order to reduce energy usage, you may need such an effective insulation layer to wrap your home yet prevent any unnecessary issues up there. On the other hand, if you do it properly, you can definitely reduce energy loss.

    Pairing a reflective insulator with a layer of radiant barrier will help to make your home always feels comfortable without consuming a high level of energy. Also, you can save a huge amount on electricity bills.

    No matter it is an office or a home, a layer of metal roof insulation will give you a lot of benefits. The layer can be installed over the existing shingles, new roof decking, or simply over open rafters.

    Adding the metal roof insulation can be done easily when you renovate your house. You will need to hire some well-trained roofing insulation experts to make a more energy efficient home. Or you may also consider metal roofing over rigid insulation details even though it might be a bit pricier.

    From all the roofing materials we have explained above, you are in charge of choosing which one is the best one and most suitable for your building. Other than that, some people also consider the financial thing before choosing one of them. In the end, this is anything you need to know when it comes to metal roof insulation.

    Two Major Types Of Flat Roof Insulation

    As mentioned previously, there are two major types of flat roof insulation. The first one is the cold roof insulation. This is when you insulate your flat roof from the inside. On the other hand, the second major type of flat roof is warm roof insulation, which is the exact opposite of cold roof insulation because, in this case, you will insulate your flat roof from the outside. At this point, we will now go to the specifics and the helpful techniques on how to insulate a flat roof from the outside and from the inside.

    Cold roof insulation is more commonly used by many homeowners since it is much less expensive as compared to warm roof insulation. In this type, the insulation is snugly placed underneath the roofs surface and in-between the joists. To be more specific, you will have to put the insulation between each of the supporting joists and leave a gap in each for about fifty to sixty millimeters. On the other hand, if you are going to replace the insulation in your current flat roof house, one recommended piece of advice is for you to take down your ceiling too to ensure proper installation. Also, in the case of a shallow joist above your ceiling, the best way is for you to use spray foam as your insulation.

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    What Flat Roof Insulation Should I Use

    Using insulation board in a flat roofing insulation build-up is a widely accepted industry standard as its one of the best weight-bearing insulation types. Whether the flat roof being installed will be walked on or not, flat roof insulation board typically has a hard-faced surface and good compressive strength both for extra stability and extra adhesion for the waterproof membrane.

    Kingspan and Recticel are the two of the most well-known flat roof insulation brands and theyre firm favourites of Insulation Superstore customers.

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

    Flat Roof Ceiling Insulation

    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, we’ve found that a foam-free solution is possible.

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