In recent years, it has become more and more common for home owners to demand that their patio paving is laid at the same level as the doors and other thresholds as their interior flooring, thus creating a seamless hard landscaping ‘carpet’, often requiring the same product, laid on the external patio as used on the internal flooring – usually tiling thickness porcelain or ceramic units, matching the same colour and pattern to give an impression of infinity paving.
Owners demand that designers work on the brief of this seamlessness, without having any insight or knowledge of the technical factors and techniques used in the construction of their houses. They have seen it in magazines, their friends have something similar, and they want the same – even if their house if fifty years older than their friends new-build unit.
Designers, often reluctant to disoblige, go ahead and produce drawings and plans showing the same tiling throughout, even colour matching and instructing the contractor to use the same tiles including the manufacturer’s product code numbers and source of the original products.
Thus, the homeowner becomes encouraged to think that they can have this seamless effect without any problems. The designer or owner duly involves a contractor, either as a Builder or Landscaper, and charges them with constructing the scheme, somehow making it work – even if the designer has not produced any cross sectional or technical drawings showing how this is to be achieved.
All new build houses must be designed and constructed for use by ambulant disabled people and wheelchair users, to allow for the person to approach the entrance and either turn to face the door, or achieve unimpeded access from one surface to another (there is a 15mm upstand allowed, if the edges are rounded) i.e. from indoors to outdoors or vice versa.
It does not follow that older buildings – indeed, it would be unusual unless new patio doors have been fitted retrospectively – will have been designed to the same standards as new builds (not necessarily in build quality, but in the technical detailing). Older properties are not able to achieve this seamlessness without special ramping to maintain a minimum of 150mm between the paved surfaces and the damp proof course membrane (d.p.c.) to prevent water from gaining ingress to the brickwork above d.p.c. or by rainwater splash. I will discuss these later in this article.
Building
Regulations
Level Thresholds and Water Ingress Statutory Requirements
In England and Wales, the Building Regulations Document M Clause 6.19 is effective in the matter of thresholds and water ingress. This information is easily obtained from the Internet, but understanding how the subject effects the landscape industry is less clear. Anecdotal evidence is passed from one designer to another, landscapers discussing the topic unable to agree, because essentially, the type of property is less important as to how it was designed and constructed having due regard to water ingress and disability.
Put simply, the design of the internal floor and construction techniques employed in the house build and door type are critical. Unless the main building has been designed to permit such unimpeded access, with a series of special barriers and configurations to prevent not only water ingress, but also thermal insulation (to prevent capillary action or water ingress through hot air within the building, drawing moisture into the floor construction), no amount of external designing can mitigate potential problems with moisture.
The external approach to an entrance should consist of a reasonably level platform or ramp to provide an accessible threshold. This should slope away from the building by between 7 and 15 degrees to prevent rainwater from building up or being driven towards the building.
The threshold design must satisfy the provisions of The Building Regulations in respect of minimising the risk of water ingress or damp entering the building (Part C). This regulation goes on to mention vitally important elements of the house construction, that if a designer wishes to create a seamless vista, they should first of all contact the Architect of the building to obtain written instructions or receive a copy of the internal floor plans and cross-sectional drawings as used by the main Builder during construction works.
The internal floor must have been installed using adequate sub-flooring ventilation, with thermal insulation to ensure there is no thermal bridging (i.e. capillary action as described above). An internal perimeter insulation strip must be installed as part of the construction, together with a non-deformable insulated cavity between the brickwork and cavity insulation. This feature is to be found under the floor screed level.
In other words, the interior design of the floor and threshold must have been designed to allow for wheelchair access. The job of the designer is to ensure that nothing takes place outside the house walls that could compromise the design of the internal flooring/threshold.
It is permissible to install a channel, at least 63mm wide as a semi-circular unit, open at least one end, freely discharging into an adequate system to allow water to leave the channel cleanly and without impediment or allowing water to enter and remain within the channel. Both ends of the channel must be free draining, either into a rain water drain or across the fall of the garden, without discharging rainwater on to a neighbouring property in an obvious manner.
This channel must be set into lean mix concrete, with a cross fall of 1:60 to discharge water. There should be a gap between the external paving and door threshold of a maximum width of 18mm to prevent disability equipment e.g. walking sticks, from becoming trapped in the groove.
In essence, the works designed into a new build house, allowing for wheelchair access, may be continued in the garden and landscaping schemes. Using the same logic and technical detailing, an external means of preventing water from laying against the house walls, allowing adequate drainage away from doors and patio windows, the designer should ensure that there is no compromise between the Architect’s intentions and the owners wishes. If in doubt, the Architect or Builder should be pleased to work with you as a designer or design and build contractor to advise you on the internal makeup and compliances required to avoid breaching Building Regulations. It is in their interests to do so, as the new-build will be under an NHBC warranty for many years to come!
Bear in mind that timber thresholds may have a shorter life span than polyurethane or other plastic compounds, and it is essential that the wood remains free of standing water.
Older Properties
When asked to achieve the same seamless paving scene on older properties, it is essential that some alternative logic is required. Older houses may not have the same Building Regulation restrictions regarding wheelchair and disability compliances, the most significant of which is the maximum gap of 18mm between the paving and threshold. This difference allows the designer to consider wider and more creative methods of preventing moisture from becoming a problem.
As every site is different, with levels, falls, crossfalls, soil types and drainage, slope and size/area of ground beyond the immediate threshold/patio doors/doors there can be no hard and fast rule pertaining to designing a seamless visual from interior to exterior flooring for a garden design.
Obviously, by using the same products internally and externally it is possible to achieve a universal visual appearance in the paving (although laying methods will vary. Internal Tiling comes under BS 5385 which involves different techniques including a waterproof membrane for internal floors, and laying of paving, which falls under BS 7533, and is another subject altogether!) These variations may manifest in different jointing gaps, and it may be difficult to marry straight lines in a design or pattern if the joints are wider/narrower.
The damp proof course membrane level difference between the hard paving and dpc are 150mm, ( Building Regs ; see above) and any raising of that level must be carried out in a way that protects the building from rainwater. Bear in mind, the new build houses have a host of internal protective features as mentioned previously, and the brickwork of the structure may not be protected by any insulation barriers in older houses.
Beware of suspended floors in buildings. These may be indicated by the fact that air bricks are situated under the damp proof course membrane, so that air may freely pass under the building to prevent damp issues. It is technically very difficult to achieve seamless floors with such properties, and will certainly require expert opinion and specification, skills that fall outside the insurance cover provided to garden designers!
Therefore, all protective methods must be carried out externally. These may manifest themselves in different ways. On some sites, provided that the thresholds are designed to prevent water ingress whilst affording a seamless level between interior and exterior paving, the levels across the house walls will require a graduated system to return the laying levels to 150mm below dpc, or seek another method of achieving the same effect i.e. preventing rainwater from laying against the walls, and alleviating rain water splash from making the brickwork damp.
There is a wide range of decorative metal channel covers available in various patterns, to cover drainage channels set 150mm below dpc to accord with the Building Regulations. Other channels may be filled with rounded pebbles (rounded to reduce rain water splash) to a depth of at least 150mm, ensuring they are free draining as previously discussed. These methods should be discussed with the Local Authority Planning Department to ensure that you do not fall foul of their regulations (some are more relaxed than others, but ensure you get their ruling in writing. This is NOT a waiver, but an Approval Document)
Summary
To summarise, the requisite for designing seamless, same level paving/tiling patterns from internal floors to external patios and paths will involve research and due diligence on the part of the Designer or Design & Build Contractor.
The first step is to carry out a complete survey of the exterior of the property, paying attention to existing drains and the potential to discharge rain and surface water away from the house walls, at the same time evaluating the potential for storm water from causing problems with water ingress. Look well beyond the immediate area under discussion to gain a general overview of the site.
Ask to inspect the Architects drawings and cross-sectional plans from the builder (if known).
These documents should be referenced on the designers plans as evidence of due diligence.
Under no circumstances should the designer accept a verbal or written waiver from the customer by means of mitigating your responsibilities. (See Waivers elsewhere in The Landscape Library), as by accepting such a document it will indicate that you knew there was a problem, but chose to ignore it one the say-so of an amateur (the customer) As the Professional Designer, and Principal Designer under CDM Regs 2015, you will be deemed to be the Expert should any future claim arise through your actions.
There is plenty of detailed information available from the website, including cross sectional drawings, which should be carefully noted. The points I have raised above go beyond those advisory notes, as I have been dealing with Claims cases and Disputes as an Expert Witness for many years now, and have seen too many designers turn a blind eye to potential problems, only to find themselves in financial trouble once a project fails. These failures manifest themselves in different ways, but always involve damp ingress, mould, rotting floors, ruined carpets, furniture and fittings, plus claims on health grounds.
Alan Sargent
