BYTNAR - TALKS
EPISODE 012 - APPROVED DOCUMENT A - STRUCTURES - PART 1
This episode is for people who want to know more about Approved Document Part A - Structure.
You should like this episode if you ask yourself questions like:
What are the key structural safety requirements outlined in Approved Document A of the Building Regulations?
How does Approved Document A address loading requirements for traditional construction?
What measures are recommended in Approved Document A for managing ground movement, like soil subsidence?
What are the guidelines for the stability of timber and masonry structures in the Building Regulations?
How should connections between walls, roofs, and floors be designed according to Approved Document A?
What are the specifications for wall cladding and roof coverings to ensure structural integrity?
How should builders ensure that roof fixings withstand wind loads and environmental stress?
What are the regulations for addressing disproportionate collapse in existing buildings under Approved Document A?
How does Approved Document A assist architects and engineers in selecting suitable materials for construction?
This is Bytnar Talks the Engineer Takes on Construction Episode 12 hi I'm Piotr Bytnar each day I help my clients plan and design building projects through Bytnar Limited a Consulting Chartered Structural Engineers practice my biggest passion and the corner stone on which I've built my business is find finding clever solutions for construction projects I am a chartered structural engineer and a bing software developer so you can rest assured that I will strive to talk about the best practices and the use of new technologies in the industry and if you're embarking on a construction project or are involved in planning designing and building the world around us you'll find this podcast useful approv documents structure part one [Music] hi there and welcome back to the bitnar talks your favorite podcast on all matters of architecture engineering and construction it is Thursday the 11th of August 2024 and I'm here back with you with the 12th episode and further information on approved documents it has been a busy week we help people achieve their planning permissions and for full plan approvals for building control and visited some dangerous structures to assess under conditions I shot some pigeon clay as part of the local Kent networking group closed new clients and managed to do it all while preparing this podcast for you what would my childhood hero say who does not love it when the plan comes well together last week in the episode 11 I took you on the journey through all approved documents and how it all comes together there are 18 requirements with 17 approved documents as requirement n highs within approved document K and there is an additional document that deals with materials and workmanship I will now move us to more detail within the first requirement structure all right let us unpack it all a bit so without further Ado let's dive into the structural requirements of the approved document [Music] the purpose of this material is to give you a general appreciation of the requirements put on You by approved documents the approved documents form the primary source of the information prepared by the Secretary of State describing how the building regulations requirements can be discharged these form guidance for register building control approvers to discharge their duties so the first thing they will do will would be to take your project and dissect it Point by Point taking all the necessary boxes identified within the [Music] document in this episode I will talk about the first consideration within the schedule of requirements identified in the building regulations 2010 which is structure there are three consideration brought up by the regulator which is A1 loading A2 ground movement and A3 disproportionate collapse in the main part of this episode I will talk about the first two aspects loading and ground movement and I will leave that this proportionate collapse for its own episode within which will form part two of the approved documents structure I will Begin by telling you how the do is structured and we'll go Section by section giving you simple reasons behind the text and my commentary all right let's get on to [Music] it so the approved document a is put in place to give practical approach to the meaning of the building regulation requirement a I will read it for you now now so you can appreciate how broad it is so the regulation says loading A1 paragraph one the building shall be constructed so that the combined dead imposed and wind loads are sustained and transmitting transmitted by It To The Ground sub paragraph a safely and B without causing such deflection or deformation of any part of the building or such movement of the ground as will impair the stability of any part of another building paragraph two in assessing whether a building complies with sub paragraph one regard shall be had to the imposed and wind loads to which it is likely to be subjected in the OR ordinary cause of its use for the purpose for which it is intended and aspect two ground movement A2 the building shall be constructed so that ground movement caused by a swelling shrinkage or freezing of the subsoil or sub paragraph B land sleep or subsidence other than subsidence arising from shrinkage in so far as the risk can be reasonably foreseen will not impair the stability of any part of the building so here we have it you can appreciate this is quite General and close to possible to make the same sense with anyone else than with than with it with yourself what I mean by that I may have a different approach to yours and you may have different approach to mine to me requirement regarding loading is simple the structure must be safe on its own itself for ordinary circumstances and cannot unduly impact any other structure and the requirement regarding ground movement simply States the building needs to be placed on sound enough ground so any movement will not impair that building's stability simples so as long as the building is safe and stable and does not impact the neighboring buildings it is fine to the letter of the law but what does that mean exactly no one knows and no one assigns their judgment to it at least the regulator does not as however detailed and prescriptive their approved documents may appear they begin with the information that there is no obligation to adopt them if we want to discharge the requirements in other way no the regulator or registered building control approver will be liable for the use or insistence of any particular solution from that document unfortunately the approvers have the power of veto and the only way they can judge on The Proposal is often approved documents only so the principal designer will be in most cases restrained to the use of these documents so let us see what is this document about the approved document approach is the requirement of structural safety by listing the possible documents that are also approved and applicable and the latest revision of these documents should always be taken into consideration and that is section one it allows us child Structural Engineers to use this information use the years of knowledge and experience to create any given to specify any any needed project out there started from small projects like described in this this approved document going through hospitals offices multi-use highrise tunnels and bridges just to name a few then the approved document goes on to giving directions for sizing of elements in traditional buildings to carry load and wind in section two section three deals with wall clading and section four deals with roof covering all these sections address requirement one and two of the regulations as mentioned before requirement three the disproportionate collapse of buildings will be talked about in the next episode as I think it requires its due consideration and more attention there are 23 diagrams and 10 tables that accompany the text of this document and assist you in understanding and discharging their requirements it should be noted that the old British standards are no longer approved where substituted by Euro code alternative but in practice I have not seen an officer who would not approve all standards if these are presented to them I've received documentation that bases its design on standards going back half a century and these were approved I'm interested if this will change now with the onset of building safety act and the requirement of competence anyhow the list of approved standards can be found in the document and it is prudent to refer to these standards as forming argumentation for your design decisions the list contained within section one concerns ways to approach structural analysis and design and typical loadings and actions that this may be subject to and all typical and codified design circumstances covered by Euro codes their National annexes and supplementary documents covering their use and interpretation for General applications this section also references documentation requirements posed by localized ground movement things like land sleep mining instability and field ground as well as the approach to the appraisal of the existing buildings for their material change of use going into section two we are divided furly into aspects a b c d and e it should be noted that requirement a tells what to to look into and considering aspect B and C but in general all aspects B2 e can be treated independently of one another so section 2 a one states that the requirements of this this document this approved document is concerning lowrise residential buildings only and should be read with paragraph B and C traditionally in Britain buildings are made of masonry walls be it solid or cavity and Timber flows roofs engineered products are are now also widely available sub paragraph 82 limits the overall size and proportion of the building and gives restriction on layouts and cell sizes requiring walls to connect to each other either by bonding or by means of mechanical fixings and requires roofs and flaws to Prov provide lateral support capable in transferring load to bessing elements of the building so when you think about the floor or roof do not think about it in a in its traditional function of either carrying you and your gear in terms of floor or carrying roof tiles and snow but also taking consideration that these planes these floors and roofs need to connect to walls in both directions to stabilize the walls the walls other wise wouldn't be wouldn't be that stable and could collapse aspect B deals with Timber it directs us to tr tables as the span tables have been removed at one of the revisions of approved documents some years ago although engineer can easily calculate the required size and strength also it also directs us to to the necessity of treating Timber when when that can be susceptible to the presence of household long B which is usually Southeast in our country as it's dry and sunny and dry and sunny areas are the areas that can experience longor bol laras of these little creatures simply thrive on dry subw of coniferous trees of on dry supp of of soft wood trees moving on to aspect C which is masonry the approved documents follows the approve approach here the the approved documents approach here is very Broad and and the parches are possible when when proved by calculation or experience the limit of application of this guidance is considered to be for the buildings of the height not not extending more than 50 m and no more than three stories but also applies to small single story non-residential buildings like annexes carriages and out buildings the limit on the height may be more stringent though depending on the location and wind exposure of the building and the orography of the area the proportion of the least width to the height cannot be more than two according to the document so the smallest side of the building will determine the maximum height of that building and similarly with annexes if the annex protrusion away from the main building is more than two times its width the height of this Annex cannot be more than two times the smaller width this is in place to make sure the building is stocky or in other words to make it possible for floors and roofs to translate the wind loads to B tressing elements this is also evident in the limit of the flaws which area given at 70 M squared for floors and closed by all Walls by walls from all sides and fic M squ for floors with one side open you will also know that walls are limited to 12 M runs or 12 M height between supporting elements and that are its limits on the loads that are taken in consideration so if you are intending to use the space with more honorous expectations some localized strengthening will be required similar limits are put on the actual selection of the material for the wall and its thickness which should not be less than one divided by 16 and if the wall is made of UNCA Rubble it should be 1 divided by 12 so however High the wall is divided by 16 or 12 and you have the the thickness that you can use the are farther re further requirements diagrams and tables that can guide you in selection of appropriate material thickness size and and layout of your building as well as number and position of wall ties if you choose cavity wall for your project the rules of materials and its strength selection for different size of buildings and different position of walls is also provided the specification for motor to this does take in consideration the safety of the building but not its performance so it may be prudent to use other strengths in your building to perhaps mitigate on the appearance of cracks or allow for future extension there is limit on the span of floors at 6 M from the center of the bearing to the center of the bearing which basically gives you around 5.9 M between the faces of the walls which guess what if combined with the limit on the wall length give us the maximum area for the compartment at 70 M squared similar proportion to that of the parit wall is given to the retaining power of the wall for retention of soil no more than 1 M high but it needs to to be noted that the wall needs to extend for the entire story to provide enough load to resist pushing action of that soil there's also a limit to the load at the foundation of 7 tons per meter run you will find rules on bessing walls peas and chimneys openings in walls chases and recesses unfortunately masonary is weak in bending so removal of parts of panels or but resing weakens the wall and may lead to the circumstance where the wall is weaker than the window or door you put into it and the actual door or window will strengthen the wall which by the way is not the reasonable ideal thing to do as mentioned previously the walls and roof needs to provide lateral support on all sides to the walls and generally be mechanically fixed to the walls whether it is your external wall cable wall or internal wall you need to make sure they are tying the walls together at least every 2 m centers however some relaxation of these requirements are possible if there is enough contact between the wall and the floor and the building is no more than two story high you should also remember to strap the roof down to the wall at Eaves at similar distances to avoid the roof lifting up if the roof is of sufficient pitch and weight this requirement may be on committed it is good to voice the fact that if there are wall or floor openings interrupting the lateral or vertical restraint there should be Provisions in place to address this fact and enough restraint Pro provided in suitable locations the mentioned rules are relaxed a little bit when it comes to small non-residential buildings it is good to note that this should be at least 130 kg per M square of wall buildup if the outbuilding anex or garage is smaller than 10 m squared it doesn't have to be but anything over that that floor area should have enough Mass not to not to behave like a like a kite it shouldn't be bigger than 36 M squared with a maximum wall size of 9 M and of 3 to 4 and 1/2 M Maxim height 3 m for the flat roof 4 and 1 half M for the pit roof walls should be tied to the roof horizontally and vertically and P should be provided wherever needed off to aspect D Mas chimneys similar to parit walls these are referenced to be in to be not higher than four and a time four and a half times the smaller Dimension if constructed in traditional masonry of a at least 1 and 1/2 ton per M cubed density this provision is in place to account for the gravity load resistant overturning action of the wind so here we here we have it you need to have that mass so the chimney stack does not collapse when it comes down to mass concrete foundations when the mass concrete foundations are concerned they are concerned with ground ground that needs to be uniform to mitigate differential settlement and damage that can appear reveal itself as the buildings settle differential settles unevenly the mass concrete foundation strip should not be less deep than 150 mm so it shouldn't be should be at least 150 mm thick and of 10 Newtons per mm squared strength which relates to gen one concrete but designation needs to take in consideration durability too so very often in clayish or British conditions really you need to account for sulfates in the in the ground so the the foundation will very often be F andd designation some more expectations to width formation depth and stepping of the footing is noted within the document the foundation width gener generally requires no higher gr pressure than 100 K per M squared in granal soil and 50 to 75 K per me squ in cohesive soil the requirement for the foundation is usually governed by the projection requirements rather than that of the bearing pressure it is generally considered normal for the building to settle 25 mm during construction construction or in some time after the completion which may be longer than 10 years all building officers these days will ask you to identify trees nearby we are receiving requests for up to 30 m r radius despite the type of the soil this is due to the to the to the N nhbc guidance nhbc stands for the national house building ccil who in their guidance documents 4.2 building near trees go in depth in their expectations it basically boils down to two solutions if you build need trees in soil that is influenced by the variance of water you will either need to follow the nhbc guidance all have their foundations engineered from my personal experience I see how damaging to the planet this approach is people pour tons of concrete in the ground and use polysterene to mitigate impact on sites where there are trees within the limits of the guidance but their influence does not extend to the per perimeter of the sight rendering the guidance harmful this can be very often observed by assessing the existing buildings around around those trees and in even closer proximity to those trees it is quite damaging for the for the planet quite damaging for the pockets of of clients of people who wants to build buildings but maybe not for the contractors and compressive material producers and certainly not for nhbc warranty provider in general we are used to specify the dep of foundation from around half a meter deep 45 cm deep below the ground level down to 1 M but following nhbc guidance this may well go to 2 and A2 meter down or will require a rough or piled and beam Foundation off to section three which treats about wall clading that needs to be structurally sound so it does not detach and harm anyone else it also needs to be durable resistant to weather fire and passage of sound but hey one thing at the time the clouding design and design of its fixing needs to account for all the loads applied at it and the behavior thermal and moisture related fixing should be at least as durable as the studing itself and be designed developed and tested either by the specifier of the bepoke solution or manufacturer of the off the shelf solution and finally section four which similar to section three in this time deals with roof covering which needs to do a good job and neither Fly Away during incremental weather nor to collapse when accessed by repair Personnel some concessions are allow here for areas not accessed by maintenance like roof lights but that's that's done it can also be dangerous to increase the weight of the existing roof by more than 15% which often happens with with Chang in the attic space adding insulation and ceiling boarding or perhaps installing photov voltaic panels on the top of the roof Ina in which case engineering assessment will be required if that increase of weight is more than 15% of the existing weight contrary to adding weight to making the roof overloaded removing the original weight from the roof can lead to the roof lifting off for a journey to neighbor's Garden So to avoid such a predicament it may be needed to strap that roof down to the walls [Music] okay now let's summarize that a little bit shall we so so yeah the approved document a provides guidance on on ensuring the structural safety and stability of the building and its compliance with building regulations requirement a it covers aspects such as loading ground movement stability of different building elements with emphasize on traditional construction considerations are also given for materials like Timber and masonry the document emphasizes the importance of ensuring that building can withstand various loads including debt impos and wind loads without compromising safety or stability of that building or buildings nearby it also addresses ground movement caused by factors like so swelling shrinkage or subsidence to prevent any adverse effects on the building stability or more likely the adverse effects on the insurance claims against nhbc different sections of the document focus on specific aspects of construction such as stability Timber elements masonry chimneys and foundations for instance it provides guidance on selecting suitable materials and ensuring proper connections between walls roofs and Floors requirements for wall clading and roof coverage are also mentioned highlighting the needs for structural Integrity durability and resistance to external forces fixings for clading and roofing materials must be appropriately designed to withstand applied loads and environmental conditions Additionally the document addresses considerations for existing buildings undergoing a material change of use and provides guidance on addressing disproportionate collapse about which the whole part two will be treating next week so here we have approved document a serves as a comprehensive resource for Architects engineers and Builders to ensure that buildings meet regulator standards for safety and stability for small and traditional buildings however Structural Engineers can go on and design much much more using other approved standards and guidances [Music] this is the end I'm glad you stayed all the way till now I hope this episode brought to you the expectations of the proof document a and that you now know how to use that document if you have any questions reach out to me on LinkedIn or send me an email I'm more than happy to help you out you can book an on obligatory consultation on our website www.bar.ca.gov ask a specific question whether your question is if we can help you with your project or what should I do we will be able to show you the right direction at bitna we help our clients design execute their dream homes or Investments I will now take some in depth look into the disproportionate collapse of buildings requirement to deliver some simple answers to you next week for now have a great weekend and successful week ahead thank you thank you again for listening please voice up your opinions I'm waiting for you on LinkedIn and I want to hear from you Toodloo!
Piotr Bytnar BEng (Hons) MSc CEng MIStructE
Chartered Structural Engineer who deals with the Architecture of buildings. His Master's Studies led him to an in-depth understanding of risk and contract arrangements in construction as well as specialist knowledge in soil mechanics.
He and his team help homeowners and property developers to design and deliver construction projects reducing waste in time and the cost. He believes that the construction project is an iterative process that can be well managed and it is best managed if all the aspects of the project definition and management are dealt with in-house or coordinated by one organisation. His team works to all stages of RIBA and ISTRUCTE stages of work and enables contractors to deliver projects on-site providing risk evaluations, methodologies for execution of works and temporary works designs.
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