2022 changes to the building regulations for extensions (Part L) – tomspriggs
Part L of the building regulations deals with the thermal performance, or limiting the heat losses from any given building. Here, I am exploring the recent changes that affect extensions and work to existing buildings.
The legal requirement is governed by a brief few paragraphs, however there is also a suite of supportive documents called ‘The Approved Documents”. These are descriptive methods of complying with those paragraphs, and for all intents and purposes can be considered ‘the regulations’. (There can be times when methods need to step outside of these approved documents and then this distinction is more important).
Part L has undergone the most change over the last decade or so compared to the other documents as the thermal performance of buildings is a key area for improvement. (Stair safety design hasn’t changed as much for example). Recent changes until this year have solely dealt with new buildings, now extensions to existing dwellings also get a jump up in thermal performance. This is great news as improvements are desperately needed. The minimal requirements have taken a big jump up, but alas no enforced ‘consequential improvements’ have been included.
Consequential improvements already forms part of work to commercial buildings, and basically requires a percentage of the overall budget to improve the existing building as well, not just the extension. On most projects this occurs anyway as energy improvements can come from boiler upgrades, lighting etc as well as insulation, so in my mind would have been a useful tool in improving existing building stock.
The accepted method of measuring heat losses through part of a building ‘an element’ is measured in a U-value. It is an expression of heat loss through a part of a building (relevant to the temperature difference). Measured in W/m²K. The lower the number the less heat is lost. For example a typical window u-value might be 1.6W/m²K, whereas a wall in an older extension might be 0.28W/m²K, with much more heat lost through the window.
For new dwellings or higher standards such as PassiveHaus then the whole system is just, if not more, important than the individual elements. Think of a really warm jacket with terrible stitching and gaps – you lose too much to the gaps than you save by increasing the thickness of the warm bits. On extension work calculating and measuring the whole building+extension is generally regarded as too difficult / onerous as the existing building will have too great an influence. On really good designs or exemplar projects the whole house will be considered and measured so the best approach can be taken.
On most projects therefore as long as the extension meets the minimum criteria, it is deemed to pass building regulations. It is these minimums that have jumped up in requirements this year.
The amount of glazing and orientation will also influence the design as if there is a lot of glazing, then the insulation levels in the remaining elements may have to be better still to make up for it. (Calculated as an area-weighted figure).
For reference as of July 2022, (remember the lower the number the better), all in W/m²K:
- Roofs have gone from 0.18/0.16 depending on type to 0.15 for all roofs
- Walls have gone from 0.28 to 0.18
- Floors have gone from 0.22 to 0.18
- Windows have gone from 1.6 to 1.4 with glazed doors also going from 1.8 to 1.4
- Rooflights are 2.20
These will have an impact on previously ‘normal constructions’ For example a basic brick lean-to extension could have had the following construction thicknesses pre July 2022:
Roof: Artificial slates, battens, breather membrane with 120mm rigid insulation between and 25mm under the rafters of 150mm deep. Previously compliant at 0.18W/m²K.
Now the same construction would require 50mm insulation below the rafters rather than 25mm to achieve 0.15W/m²K.
Brick cavity wall: Brick outer leaf, 50mm clear cavity, 50mm rigid insulation, 100mm standard grade block, wet plaster finish. Previously compliant at 0.26W/m²K.
Now the same construction would require a minimum 90mm of the same insulation, therefore installed in a min 140mm cavity width.
Clearly there are other ways to achieve the requirements, switching to insulated timber frame, using thermal blocks, fully-filling the cavity with insulation (Not recommended in exposed sites and generally TSA doesn’t specify for this reason) but the time for 300mm overall thickness cavity walls is over. A rendered blockwork wall can be compliant if a 125mm cavity with 75mm insulation is used as the blockwork performs a little better than brickwork.
The increases of 25-50mm here and there may seem trivial on spacious sites, but the industry will need to take note to avoid being caught out in the details and costs. (For example longer wall ties will be needed, window sills, insulation thicknesses, concrete foundations will all also have knock-on increases.)
How to Decide Thickness of Masonry Walls in Buildings?
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Thickness of masonry walls in a building is designed based on loads and other factors. Various requirements for suitable thickness of masonry walls are discussed.
Fig.1: Masonry Wall and Masonry Structure
- Requirement for Thickness of Masonry Walls in Buildings
- Thickness Requirements for Load Bearing Masonry Wall
- Stiffened Masonry Wall
- Top Storey Masonry Wall
- Residential Masonry Wall
- Masonry Wall of Penthouses and Roof Structures
- Hollow Masonry Wall
- Thickness Requirements of Rubble Stone Walls
- Thickness of Non-Load Bearing Masonry Walls
Requirement for Thickness of Masonry Walls in Buildings
There are various requirements regarding the thickness of masonry walls that needs to be considered at the design stage.
For example, it is recommended to use constant masonry wall thickness between lateral supports. The lateral support for masonry is provided by cross walls, pilasters, and structural frame members as shown in Figure-2.
Fig.2: Lateral Support of Masonry Wall
Regarding variation of masonry in vertical direction, the distance between floors, structural frames and roofs should be considered when the thickness of masonry wall is varied.
Masonry wall thickness changes between floor and roof and between different floors is usually enforced to reach thermal, sound and fire requirements.
Fig.3: Vertical support of masonry wall considered for making changes in masonry thickness
If masonry wall thickness is changed, it is recommended to extend the thicker wall to the lower support level.
Building code requirements and specifications for masonry structure (ACI 530-11) states that, when the thickness of masonry wall constructed from hollow masonry units is changed, then it would be required to provide a layer or several layer of solid masonry units or completely grouted hollow masonry units between thicker masonry wall and the thinner masonry wall.
The aim of providing solid masonry course between thicker and thinner masonry wall is to properly transfer loads from the above wall (thin wall) to the wall below (thick wall).
There are several limitations and restrictions which should be considered for masonry walls except in the case where the walls are designed for reinforcements based on the engineering principles.
The limitation associated with masonry thickness for different masonry walls types are discussed below.
Thickness Requirements for Load Bearing Masonry Wall
The thickness of load bearing masonry wall should be at least 304.8 mm (1 ft.) thick for maximum wall height of 10.668m (35 ft.).
Moreover, the thickness of masonry wall need to be increased by 101.6 mm (4in.) for each successive 10.668m (35 ft.) height or fractions of this height measured from the top of the masonry wall.
There are several cases in which the above conditions may not be applied for load bearing masonry walls.
These exceptional cases involve stiffened masonry wall, top storey masonry wall, residential masonry wall, masonry wall of penthouses and roof structures, plain concrete and grouted brick masonry wall, hollow masonry wall, faced masonry wall, nonbearing masonry wall.
Stiffened Masonry Wall
If load bearing masonry wall is strengthened or stiffened by reinforced concrete floors or masonry cross walls at a distance not greater than 3.65m (12 ft.), then it is possible to adopt thickness of 304.8mm (1 ft.) for maximum wall height of 21.33m (70 ft.).
The thickness of masonry wall should be increased by 101.6mm (4 in.) for each successive 21.33m (70ft.) height or fractions of this height measured from the top of the masonry wall.
Top Storey Masonry Wall
It is permitted to use a thickness of 203.2mm (8 inch) for top storey bearing masonry of a building with ultimate height of 10.668m (35 ft.).
The wall should not experience lateral loads and its height should not exceed 3.65m (12 ft.) otherwise such thickness cannot be considered.
Residential Masonry Wall
The thickness of bearing masonry wall of in residential building with maximum three storeys can be assumed to be 203.2mm (8 inch).
This thickness should not be employed if the building is higher than three storeys, or the height of the wall exceeds 10. 668m (35 ft.), or the wall subjected to lateral forces.
Additionally, the wall thickness can be decreased to 152.4mm (6 in.) for one storey building if the maximum wall height is 2.74m (9 ft.).
Masonry Wall of Penthouses and Roof Structures
The thickness of bearing wall masonry with a height of 3.65m (12 ft.) above roof level or penthouses can be assumed to be 203.2mm (8 inch).
Plain Concrete and Grouted Brick Masonry Wall
It is possible to adopt 152mm (6 ft.) thickness of plain concrete and grouted brick masonry wall.
Hollow Masonry Wall
It is advised to restrict the height of cavity or bonded hollow masonry wall to a maximum of 10.668m (35 ft.).
Added to that, the height of cavity wall should not be greater than 7.62m (25 ft.) above the support if its thickness is equal to 254mm (10 inch).
Thickness Requirements of Rubble Stone Walls
The thickness of stone wall should not be smaller 406mm (16 in.) in any case.
Thickness of Non-Load Bearing Masonry Walls
The minimum thickness of parapet wall can be assumed to be 203mm (8 inch) and its height should not be larger than three times the wall thickness.
Nonetheless, it is possible to use smaller thickness for parapet wall if it is reinforced to resist earthquakes.
Regarding thickness requirements of exterior nonbearing masonry wall, the same specifications provided by ACI 530-11 for bearing masonry wall should be used which is 152mm (6 inch) for single storey building and 203mm (8 inch) for more than one storey building.
Read More:Types of Masonry WallsTypes of Bonds in Brick Masonry Wall Construction and their UsesBuilding Construction with Plastic Bottles- Walls, Roofs and BenefitsTypes of Earthquake Resistant Masonry Walls Construction
ACI 530-11. Building code requirements and specifications for masonry structure. American Concrete Institute. Michigan, p. C151-C152. 2011.
BIA. Empirical design of brick masonry. Brick Industry Association. Virginia, p. 2-4. 1991.
FREDERICK S. MERRITT, JONATHAN T. RICKETTS. Building Design and Construction Handbook. 6th ed. New York: McGRAW-HILL, 2001.
ICC. Florida Building Code. International Code Council. Florida, p. 21.6-21.7. 2001.
Minimum Building Wall Thickness
Masonry design codes in all countries establish minimum wall thicknesses depending on the height or number of storeys of buildings. These requirements arose even during the period of construction, when the calculation of walls for strength was not carried out. The lightest load-bearing wall structures adopted in the USA refer to the period of construction of buildings with load-bearing walls up to 7 floors in 1900-1909, when metal frames did not yet replace load-bearing walls in multi-story buildings. Very light walls are being built in France and Spain, where the warm climate has created the prerequisites for a significant lightening of the walls. In Moscow, in pre-war buildings, the walls of the upper floors were made: external – in 2 ½ bricks and internal – in 2 bricks. From top to bottom, the walls thickened by ½ brick every 2 floors.
During the first two five-year plans, we achieved a radical lightening of the brick walls. It should be noted that the lightening of the outer walls is hampered by the lack of lightweight effective wall materials for capital construction. The lightening of the internal walls was delayed due to the unreasonable limitation of the minimum wall thickness by the previous norms, which established a minimum height-to-thickness ratio of 10, which completely excluded the construction of a wall of 1 brick. Meanwhile, these walls, as the practice of foreign construction and our experiments show, have great strength and stability and can even serve as load-bearing walls for interfloor ceilings.
The current standards for the design of masonry structures set minimum wall thicknesses that are more advanced than the German standards, but still inferior to the US standards. Nevertheless, they are ahead of the practice of our construction and therefore are not a limitation, but rather an incentive to lighten the walls. Table at fig. 1 . At the same time, it should be borne in mind that the data for in Fig. 1 do not replace the calculation, but only serve to pre-determine the thickness of the walls. In all cases, a check is required by the stress calculation tab.
Fig. 1. Minimum thickness of frameless walls in cm.
When using tab. in fig. 1 there may be cases that require additional instructions, namely:
- when laying walls from materials that differ in size from bricks, wall thicknesses can be rounded down up to 10%;
- with a floor height that differs from the heights indicated in the table, as well as with high cornices and parapets, when assigning wall thickness, the total height of the building from the cornice indicated in the table should be followed;
- the table is suitable for any number of floors, and the upper part of the table is taken into account, counting the number of floors from above.
The standards indicate that when using high-strength materials: bricks of grade 150 and higher, concrete stones of grade 100 and higher on mortars of grade 30 and higher, it is allowed to deviate from the table in the direction of lightening the walls.
The minimum thickness of the walls is also not limited in cases of frequent arrangement of transverse walls or other stable structures on which the walls rest under wind loads, when the distance between these structures does not exceed the value md (for the value of m, see Ceilings and coverings of buildings, fig. 3 ).
Although fig. 1 indicates the thickness of the outer walls of 51 and 38 cm, but it does not exclude the use of lighter walls in the upper three floors, which can be obtained by thermal engineering when using effective heat-insulating materials.
For group III materials (see Ceilings and coatings of buildings, fig. 1 ), which are mainly of local importance and used in low-rise construction, practice has established minimum wall thicknesses for each material according to local conditions. For rubble masonry, the minimum wall thickness is taken to be 50 cm for bed stone and 60 cm for torn stone. The practice of construction in the Caucasus and Crimea shows that when using flagstone with two parallel beds and with good dressing, the thickness of the walls can be reduced to 35-40 cm.
Stone pillars of all materials are more restricted than walls in both flexibility and minimum dimensions. This is due to the more responsible service of the pillars in the building compared to the walls; in the event of a fire, the weakening of the pillars is greater, since the perimeter of the outer part, damaged by fire, for them, in comparison with the cross-sectional area, is greater than for walls. In addition, stone pillars have a smaller mass than wall sections, and individual accidental impacts during work and operation may be more dangerous for them than for walls. The maximum flexibility for the pillars are shown in Table. at fig. 2.
Fig. 2. The maximum height ratios in the smaller side of the section and to the smaller radius of gyration for stone pillars
For pillars made of non-studded rubble on any mortar, the maximum flexibility should not be higher than 7. The minimum sections of load-bearing stone pillars are as follows: and II groups – 38×51 cm;
For wooden floors, poles with a section of 38×51 cm are allowed only in one upper floor.
In construction practice, in some cases, for example, for decorative purposes (columns supporting balconies, etc.) or for low loads and heights (basement columns of one-story buildings), thinner columns are also used. In these cases, an increased quality of work is required and the allowable stresses are reduced by 30%.
Narrow window piers with a sectional aspect ratio of less than 2 should be considered as pillars in the limits from the lintel to the window sill in terms of ultimate flexibility and should meet the requirements of the table at 9 in the directions of the minimum section size0007 pic 2 . The minimum sections of the bearing walls must be at least:
- from masonry groups I and II – 38×25 cm;
- from masonry III – 50×60 cm.
When calculating the section and setting the dimensions of the pier, the outer quarters are not included.
Smaller unreinforced masonry piers are considered decorative and are not included in the calculated sectional area of the wall. If they serve as stone mullions dividing the window opening into several smaller ones, then the lintel should be calculated assuming that the load is transferred only to the main wide piers of the wall.
High and thin piers and pillars, the stability of which is ensured only by the presence of ceilings, coverings or lintels during the production process until the erection of these structures fixing their position, must be temporarily fixed, as indicated on the working drawings.
All listed restrictions on the section and height of walls and pillars apply only to unreinforced masonry structures. In the case of longitudinal reinforcement, the values of flexibility can be significantly increased and brought to the limits adopted for reinforced concrete structures.
How thick should the walls of a country house be?
Every owner of a house wants his building to be warm and durable. This largely depends on the correct thickness of the walls. This criterion, in turn, is formed taking into account the building material. Consider what should be the thickness of the walls of the house.
External walls perform an important function – protection from the external environment. They also play the role of load-bearing structures. There are internal and external walls. Depending on the loads imposed on them, these can be load-bearing or non-bearing walls.
Ceilings and roofing elements rest on load-bearing structures. Non-bearing are designed to divide the premises among themselves.
External walls in most cases are also load-bearing. Therefore, their thickness should be greater. As a rule, they consist of several layers and include a heater.
The thickness of internal walls is usually less, especially if these are not load-bearing structures. For such partitions, their soundproofing properties are much more important. And here it is also important to choose the right building material.
Wall material – what to choose?
Starting building a house, it is of great importance what you will build walls from. What matters is durability, comfort, economy and speed of construction. Each material has its pros and cons, so the choice is quite difficult to make.
The following types of walls are most widely used:
- concrete (foam blocks, gas silicate);
- expanded clay blocks;
It would seem that everything is simple. The thicker the wall, the better. But you shouldn’t make walls too thick. First, it is a significant overpayment for materials. Secondly, the loss of usable area inside the building. Therefore, it is much easier to calculate the optimal indicators, taking into account the climate, loads and composition of the material.
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How to determine the wall thickness correctly?
For this, the following components are taken: material, design, average temperature in the region. At the same time, the temperature in the room is taken as a basis at least 18C with a properly diluted heating system and the presence of heaters.
The table shows the optimal thickness of walls made of bricks, blocks and other materials:
In general, the thickness should not be less than 1/15 of the height of the wall, from the waterproofing section to the bottom of the floor joists.
It is possible to reduce the thickness of the walls, but in this case it is necessary to increase the thermal insulation layer. For this, mineral wool, foam plastic and other materials are used. At the same time, it is possible to place a heater not only outside, but also from the inside.
Brick size in standard version is 250x120x65 mm. The length of 250 mm is the same for all types of bricks. Accordingly, the thickness of the wall has just such an indicator. In order for the house to be really warm, this parameter is not enough. What to do?
Ideally, a brick wall should be 510 mm thick. How to achieve this? With the help of two piers of brickwork plus a heater between them with a thickness of 100 mm or more. The output is a thickness of 600 mm. This figure is quite suitable for home operation in cold regions.
Aerated concrete walls
One aerated concrete block has a length of 600 mm and a height of 200 mm. The width is different – from 300 to 500 mm. The optimal wall thickness of such material is 450 mm. Therefore, it is worth choosing blocks whose width is at least 400 mm plus finishing inside and out.
Claydite concrete houses
Expanded clay concrete blocks are a popular material that has good thermal insulation and affordable price. Its width is different – from 190 to 450 mm. The optimal wall thickness of this material is 380 mm. This means that the masonry should go in two blocks if the minimum width is chosen. Often, houses made of expanded clay concrete blocks are additionally finished with bricks. In this case, the width of the block walls can be reduced.
This material rarely has a cross section of more than 220 mm, while the optimal thickness of wooden walls should be at least 480 mm. Therefore, during the construction of such houses, the use of insulation is mandatory. This will allow you to achieve the desired heat indicators.
One of the warmest and most durable building materials. Especially if a diameter of 350 mm or more is selected. But the price is also great. At the same time, having spent once, you can later save a lot on the insulation and heating of the cottage.
The thickness of the walls of a frame house depends on the number and type of layers. The heat-insulating inner layer should not be less than 150 mm. Also, the composition of the “pie” includes drywall, cement-bonded particle boards and OSB. Finishing includes lathing, membrane film, vapor barrier and siding. As a result, the frame wall will receive a thickness of 220 mm or more.