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How To Make A Flat Roof

Costing A Professional Installation

How To Build A Flat Roof Warm Or Cold Construction. What’s The Difference?

When estimating the costs of flat roofing construction via a professional company its tricky to put together an accurate price. This is due to the differing invoicing practices of commercial roofers. Labour and waste disposal costs will vary, and VAT will also have to be accounted for.

When you approach a company for a quote they should offer a free site consultation. This will break down every element of the cost. Always get at least three comparative quotes so you can assess which one offers more value. Never just opt for the cheapest.

References play an important role too. These will illustrate the companys ability to do a satisfactory job.


Help From Roofing Professionals

When it comes to choosing a drainage solution for your flat roof, it is important to consider the cost of the system, its durability, and the type of maintenance required. Every drainage system discussed here is vulnerable to clogs from debris, but you can largely avoid this risk by using scuppers with no downspouts.

If you are not sure which drainage system will work best for your roof for your money, consult the roofing professionals of Reliable Roofing. Our technicians install and maintain all types of flat roofing and we can help you choose, install, and maintain the right drainage solution for your home or building.

Common Flat Roof Drainage Solutions

By Reliable Roofing

There are many architectural designs for homes and commercial buildings that incorporate flat roofing. A flat roof not only works with the aesthetic of many building designs, but it is also durable and resistant to environmental factors that can lead to roof damage such as wind, hail, and animals. Flat roofing in residential settings may also be used for an outdoor living space or rooftop garden, adding a unique element to the building.

The one challenge with flat roofing is ensuring proper drainage. Unlike other roofing types that are slanted or sloped to allow water to drain automatically, flat roofs need a built-in drainage system to help remove moisture and debris. Poor drainage can lead to serious issues with flat roofing, from leaks to structural damage. There are several drainage solutions available for flat roofing and it is important to consider the pros and cons of each system before making a decision. This guide explains the advantages and disadvantages of the three most common flat roof drainage solutions interior drains, gutters, and scuppers.

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What Pitch Is A Flat Roof

If flat roofs are to work well, they have to have a slope, known as a fall, to shed rainwater. The fall should never be less than 1:80 and preferably about 1:40. There are several methods of building in a fall:

  • One is to set the cross walls at different heights. Most people shy away from this because they dont like the idea of having an internal ceiling that slopes
  • A far more common method is to use firring strips, which are battens cut at an angle and placed on top of the roof joists
  • Another possibility is to cut a fall into the roof insulation, something several businesses now offer its often referred to as tapered insulation

What Size Joists Are Required For Flat Roof


When calculating the size of the joists required for a flat roof, you will need to take into consideration a number of factors. You need to ensure that the joists are going to support the weight of the roofing materials. Weather conditions also need to be taken into account as the joists will need to be durable enough to withstand any harsh conditions or any added weight from snow fall. Check the BS EN 1995 code for guidance on choosing the right joist sizes.

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S To Take If Youre Concerned About Your Roof

Now that youre aware of how snow affects flat roofs and how to shield it, the next step is working out whether you should repair or replace it. Its generally more cost-effective to replace than repair old roofing. Chances are youll end up spending more in the future by constantly repairing a roof that isnt offering optimal efficiency. By selecting a quality product and having it installed by professionals, you protect your building for years to come.

Even though you may have taken care of your roofing in the past, it will need special attention to ensure it protects your building through the winter. Maintaining your flat roofs integrity requires effort and is a year-round job. With these tips youll hopefully be able to take preventative measures to make sure your flat roof handles the stress that winter weather brings with it.

Layers Of The Flat Roof

  • The first layer is laying a vapor barrier which protects the insulation layer from absorbing moisture. A vapor barrier is usually made of a polymer-bitumen film reinforced with fiberglass which are attached to the concrete screed. The edges of the film are placed vertically. Overlapped seams are carefully sealed.
  • Put a heater on a vapor barrier. If you intend to make a lightweight roof the polymer insulation is fastened directly to the vapor barrier.
  • The most important layer for a flat roof is a moisture insulation layer. The best choice is a membrane or polymer-bitumen materials.

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How Moss Can Affect A Flat Roof

Problem: Without an adequate fall on your flat roof, water can accumulate in puddles laying on the surface of the roof.

Seeds and spores can drop into this fertile environment and in no time at all, the flat roof is covered in moss and even weeds. The moss in particular holds on to the water every time it rains and when wet doubles the weight on your roof.

This weight leads to sagging of joists which in turn leads to splitting of the roof covering.

A moss covered flat roof can lead to sagging joists and leaking roofs

Solution: Add firring pieces to the roof to increase the fall and keep the roof free of moss.

Fibreglass and rubber flat roofs are far less likely to attract the same amount of moss and weeds that felt will especially if some effort is made to keep them free from grime.

A modern EPDM rubber or fibreglass roof with firring pieces can prevent water buildup and moss growth

Preventing Leaks At Abutments And Parapets

Flat roof framing diy

The most common source of leaks when it comes to flat roofs is where the flat roof meets the house or parapet walls. Turning the roof covering up the wall to form a skirting is the commonly applied method of ensuring a water-tight seal. This should be factored in when considering flat roof construction details.

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Examining Flat Roof Myths What Are The Drawbacks

Flat roofs are hard to replace

Some observers suggest its harder to replace a flat roof than a traditional pitched shingle roof because of the labor required to remove its layers . But now, flat roofs often are constructed with fewer layers because of improved waterproofing technology. This could mean flat roofs may not raise the same red flags they used to among prospective homeowners who may want to replace or remodel the roof once they move in.

Prone to water damage or leakage

Many of the potential problems a flat roof may attract such as water pooling, leakage and resulting rot or damage are due to poor installation or poor maintenance. Pay careful attention to the roof at the construction phase and throughout its lifecycle to help prevent these problems in the first place.

Solve Problems With A Commercial Roof Repair

Tired of ponding water problems? Increasing energy bills? You dont need to change your entire roof to solve issues. Local commercial roofing contractors like us will inspect your roof and determine the extent of the damage. We even conduct energy audits. We take a conservative approach by suggesting a quality commercial roofing repair.

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Installing The New Materials And Roof Covering

The last step is to install the new framework that will effectively support the flat roof sheathing. Without going into details, your first option is prefabricated roof trusses with the appropriate slope. Alternatively, you can create the slope on flat roof trusses or with slope insulation or lumber.

You will then have to cover it with a manufacturer-approved support panel before installing a new waterproofing membrane.

Watch The Wildlife In Your Roof Garden


Would you like to create more outside space but youre not sure where and how? Do you have a flat roof? If so, you could soon be enjoying additional outdoor living and entertaining space!

t is far easier than youd think to convert a flat roof into a terrace or balcony you just need to have the right materials. For example, what is your existing flat roof made of? If it is constructed of traditional felt, attempting to upgrade it into a terrace or balcony is not recommended. Flat felt roofs have a short life span many house insurers refuse to cover older felt roofs. Over the years, they are affected by the elements, blistering, cracking and attracting moss and algae. The last thing you want is to construct a beautiful new outside living space, only to find that it needs to be dismantled so that you can access the felt to make repairs.

You will be expecting your flat roof to bear more weight, which means that you must consider the implications of this extra load before building commences. By engaging the expertise of a structural engineer to advise on how your flat roof can support whatever materials you decide to use patio slabs or decking you can save yourself a lot of hassle and money further down the line.

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To Get Rid Of Ponding Water Problems

Flat roofing systems come with benefits and drawbacks. When it comes to the disadvantages, some property owners are being pestered by leaks. Unlike sloped roofs, flat roofs are susceptible to ponding water. Water that stays on a flat roof after it rains will weaken the material over time. Eventually, water penetrates the building.

Flat roofs should have a minimum slope to allow water to run off. However, in some cases, building owners hire contractors that poorly designed the roof.

Now you might be wondering why some flat roofs leak. One reason is that they have an inadequate pitch. Building owners who arent careful tend to hire roofing contractors that poorly design their roofs. Its also possible that they used subpar materials. We can see here that quality workmanship and materials matter.

How To Make A Flat Roof Have A Pitch

Commercial property owners and managers in Toronto ON would sometimes think about adding pitch to their flat roofs. If youre considering the same thing, Cox Roofing Systems is here to tell you that this project is difficult but it can be done.

This guide will cover the following essential points:

  • Typical reasons to add slope to your flat roof
  • How to make a flat roof have a pitch step by step process
  • The downsides of flat roof to pitched roof conversions

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How To Build A Shed With A Slanted Roof

The completed shed with a slanted roof image first. Slant roof style is also known as a skillion, shed or lean-to. It is a single sloping roof and can be thought of as half of a pitched roof.

When I was in the process of moving to my new house, I knew that I couldnt take my shed with me. It was my first one! It was a 6×8 beauty with a gable roof and a double door. It took almost 6 months for me to complete. I was devastated!

To make up for my loss, I consoled myself with the knowledge that Id need to build a new storage shed to house all my stuff. Id accumulated a snow blower, lawn mower, generator and much more. It would be my second shed in 2 years. My new baby!

In this post, Ill walk you through the step-by-step process of building my new shed from scratch.

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Flat Roof Replacement Cost

How to construct a garden room timber flat roof

Converting a roof is a pretty big project that will potentially affect the architecture and stability of your homes existing structure. It could even cost up to $30,000 if you go for a particularly complex replacement. Therefore, its a good idea to closely examine the issues youre dealing with and determine whether or not a new roofing system is really the best option before you begin a massive construction project.

For instance, if your main concern with your roof is moisture exposure or frequent maintenance, installing a newer, higher quality roofing membrane may be a simpler and more affordable choice. Look for a roofing contractor who has experience working with flat roofs and who knows how to add waterproof coatings and other surface treatments properly to prevent water exposure.

However, if you prefer the appearance of a pitched roof, are concerned about your existing roofs structural stability, or need roof repair to correct leaks, cracks, or other issues, your best bet may be converting to a pitched roof.

via Creative Joinery

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The Value Of Insulation And Vapor Retarders

Insulation is a vitally important component in roof systems, serving several ancillary functions in addition to the primary purpose of energy conservation, often leading to a reduction in heating and cooling costs. Insulating materials are designed to reduce the flow of heat, either from or into a building and generally installed either just below or immediately above the roofing membrane, depending on the roofing system employed. Insulation types include rigid or semi-rigid boards or panels of extruded or expanded polystyrene, polyisocyanurate, fiberboard, fiber glass and various composite insulations.

Polyisocyanurate is a closed-cell, rigid foam board insulation used in roof and wall assemblies within commercial and residential buildings of all types. Because of its high thermal performance, it is the product of choice for energy-aware architects, specifiers, builders, building owners, contractors and consumers. As one of North Americas most widely used, readily available and cost-effective insulation products, Polyiso has been cited by the U.S. Environmental Protection Agency for its responsible impact on the environment. As an example, IKOTherm Insulation and Cover Boards are dimensionally stable and compatible with a variety of roofing systems.

Other Important Considerations

Additional Resources:

For those interested in learning more about residential flat roofs, please see IKOs guide to residential flat roofs.

Keeping The Moisture In

Now onto the soil and compost goodness!1. Roll out the moisture blanket keeping a 6-8″ space around all of the edges 2. Put another layer of small stones over the moisture blanket3. Put large gravel or pebbles around the edge of the roof in the space you’ve left – this is to ensure drainage at the bottom, and also stop the plants growing into the building4. Use flashing tape to seal the pond liner to the edge of the building where there is no flashing – this makes sure that no water gets under the pond liner

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Flat Roofs Are Everywhere But What About Homes

Flat roofs are a familiar sight throughout North America. Any typical mall, warehouse, apartment building or school usually features a flat roof. This roof type is easier to install over large surfaces and is the most common choice for commercial, industrial and institutional buildings.

From the start, youll likely have questions, including: is a flat roof the right choice for a home? Is it more expensive that a steeper pitched alternative? Is it harder to install? What about ongoing maintenance?

Whether choosing a roof design for a new home, or replacing/repairing a current flat roof, IKO Industries offers much of the information needed to make informed decisions for a lasting, sturdy cover for your investment. Explore the following guide to answer many of your flat roof-related questions:

Effective Ways To Drain Your Flat Roof

Hillside Renovation: 27. The garage gets a roof.

Picture this: your home has a rooftop garden decorated with your favourite plants. It is the perfect place for simple walks. This is of course only possible when you have a flat roof. However, weather can damage it. Cracks, leaks and blisters are just a few of the problems commonly associated with this type of roof. Does that mean you have to give up on your rooftop garden? Not at all. You can install a flat roof, but you will have to maintain it to avoid damage.

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Sizes Of Joists Needed For Flat Roof Construction

As you may imagine there is a fair amount of weight involved here, in terms of boards, felt etc. so any timber joists that are used need to be strong enough to support this weight. To ensure that these timbers are strong enough for the span they have to cover a formula is used to calculate the correct width and height that the joists should be.

Additionally as part of the Building Regulations Approved Document A for structure further calculations are required to take into account additional loads such as snow that some roof may be subjected to. In most cases this depends on the area of the country the property is in and also on the ordinance datum of the property above sea level.

Due to these factors it is very important that before construction begins that you gain building regulations approval.

To aid you with this, there are 8 maximum span tables in the building regulations, which deal with the loading and span of the roof together with any slight pitch over 10 degrees that it may have to dispose of rainwater.

You can see the joist span table at the following link on the DIY Doctor website where we discuss how to remove a load bearing wall and make sure joists are the correct size to span openings.

These tables and rules are designed to protect your home. A copy of these rules can be obtained by ordering from or telephone 0870 600 5522. Fax orders are taken on 0870 600 5533. The booklet costs £10.00.


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